Publications

2022

• MOVES - V. Modelling star-planet magnetic interactions of HD 189733
  
  • Strugarek A.
  • Fares R.
  • Bourrier V.
  • Brun A. S.
  • Réville V.
  • Amari T.
  • Helling Ch.
  • Jardine M.
  • Llama J.
  • Moutou C.
  • Vidotto A. A.
  • Wheatley P. J.
  • Zarka P.
  Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2022, 512 (3), pp.4556-4572. Magnetic interactions between stars and close-in planets may lead to a detectable signal on the stellar disc. HD 189733 is one of the key exosystems thought to harbour magnetic interactions, which may have been detected in 2013 August. We present a set of 12 wind models at that period, covering the possible coronal states and coronal topologies of HD 189733 at that time. We assess the power available for the magnetic interaction and predict its temporal modulation. By comparing the predicted signal with the observed signal, we find that some models could be compatible with an interpretation based on star-planet magnetic interactions. We also find that the observed signal can be explained only with a stretch-and-break interaction mechanism, while that the Alfvén wings scenario cannot deliver enough power. We finally demonstrate that the past observational cadence of HD 189733 leads to a detection rate of only between 12 and 23 per cent, which could explain why star-planet interactions have been hard to detect in past campaigns. We conclude that the firm confirmation of their detection will require dedicated spectroscopic observations covering densely the orbital and rotation period, combined with scarcer spectropolarimetric observations to assess the concomitant large-scale magnetic topology of the star. (10.1093/mnras/stac778)
  DOI : 10.1093/mnras/stac778
• Kinematical higher-twist corrections in $\gamma^* \gamma \to \pi \pi $
  
  • Lorcé Cédric
  • Pire Bernard
  • Song Qin-Tao
  , 2022. We apply the Braun-Manashov technique to improve the description of $\gamma^*(q_1) \gamma(q_2) \to M(p_1) M(p_2)$ amplitudes at large $Q^2=-q_1^2$ and small $s=(q_1+q_2)^2$. We derive the kinematical higher-twist contributions of order $s/Q^2$ and $m^2/Q^2$ to the helicity amplitudes and estimate their sizes in the kinematics accessible at Belle and Belle II.Since pion GPDs cannot be directly measured by experiment, $\pi \pi$ GDAs are the best way to investigate the energy-momentum tensor form factors for pions.
• Electronic structure of rare-earth mononitrides: quasiatomic excitations and semiconducting bands
  
  • Galler Anna
  • Pourovskii Leonid
  New Journal of Physics, Institute of Physics: Open Access Journals, 2022, 24 (4), pp.043039. Abstract The electronic structure of the rare-earth mononitrides Ln N (where Ln = rare-earth), which are promising materials for future spintronics applications, is difficult to resolve experimentally due to a strong influence of defects on their transport and optical properties. At the same time, Ln N are challenging for theory, since wide semiconducting 2 p and 5 d bands need to be described simultaneously with strongly correlated 4 f states. Here, we calculate the many-body spectral functions and optical gaps of a series of Ln N (with Ln = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) by a density-functional + dynamical mean-field theory (DFT + DMFT) approach treating the correlated Ln 4 f shells within the quasi-atomic Hubbard-I approximation. The on-site Coulomb interaction in the 4 f shell is evaluated by a constrained DFT + Hubbard-I approach. Furthermore, to improve the treatment of semiconducting bands in DFT + DMFT, we employ the modified Becke–Johnson semilocal exchange potential. Focusing on the paramagnetic high-temperature phase, we find that all investigated Ln N are pd semiconductors with gap values ranging from 1.02 to 2.14 eV along the series. The pd band gap is direct for light Ln = La…Sm and becomes indirect for heavy rare-earths. Despite a pronounced evolution of the Ln 4 f states along the series, empty 4 f states are invariably found above the bottom of the 5 d conduction band. The calculated spectra agree well with those available from x-ray photoemission, x-ray emission and x-ray absorption measurements. (10.1088/1367-2630/ac6317)
  DOI : 10.1088/1367-2630/ac6317
• Spin dynamics of itinerant electrons: Local magnetic moment formation and Berry phase
  
  • Stepanov E.A.
  • Brener S.
  • Harkov V.
  • Katsnelson M.I.
  • Lichtenstein A.I.
  Physical Review B, American Physical Society, 2022, 105 (15), pp.155151. The state-of-the-art theoretical description of magnetic materials relies on solving effective Heisenberg spin problems or their generalizations to relativistic or multi-spin-interaction cases that explicitly assume the presence of local magnetic moments in the system. We start with a general interacting fermionic model that is often obtained in ab initio electronic structure calculations and show that the corresponding spin problem can be introduced even in the paramagnetic regime, which is characterized by a zero average value of the magnetization. Further, we derive a physical criterion for the formation of the local magnetic moment and confirm that the latter exists already at high temperatures well above the transition to the ordered magnetic state. The use of path-integral techniques allows us to disentangle spin and electronic degrees of freedom and to carefully separate rotational dynamics of the local magnetic moment from Higgs fluctuations of its absolute value. It also allows us to accurately derive the topological Berry phase and relate it to a physical bosonic variable that describes dynamics of the spin degrees of freedom. As the result, we demonstrate that the equation of motion in the case of a large magnetic moment takes a conventional Landau-Lifshitz form that explicitly accounts for the Gilbert damping due to itinerant nature of the original electronic model. (10.1103/PhysRevB.105.155151)
  DOI : 10.1103/PhysRevB.105.155151
• Notes on tensor models and tensor field theories
  
  • Gurau Razvan
  Annales de l’Institut Henri Poincaré (D) Combinatorics, Physics and their Interactions, European Mathematical Society, 2022, 9 (1), pp.159-218. (10.4171/aihpd/117)
  DOI : 10.4171/aihpd/117
• Charge self-consistent electronic structure calculations with dynamical mean-field theory using Quantum ESPRESSO, Wannier 90 and TRIQS
  
  • Beck Sophie
  • Hampel Alexander
  • Parcollet Olivier
  • Ederer Claude
  • Georges Antoine
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2022, 34 (23), pp.235601. We present a fully charge self-consistent implementation of dynamical mean field theory (DMFT) combined with density functional theory (DFT) for electronic structure calculations of materials with strong electronic correlations. The implementation uses the Quantum ESPRESSO package for the DFT calculations, the Wannier90 code for the up-/down-folding and the TRIQS software package for setting up and solving the DMFT equations. All components are available under open source licenses, are MPI-parallelized, fully integrated in the respective packages, and use an hdf5 archive interface to eliminate file parsing. We show benchmarks for three different systems that demonstrate excellent agreement with existing DFT + DMFT implementations in other ab initio electronic structure codes. (10.1088/1361-648X/ac5d1c)
  DOI : 10.1088/1361-648X/ac5d1c
• Ultrafast laser generation of over-critical, nano-plasmas inside dielectrics
  
  • Hassan Mostafa
  • Ardaneh Kazem
  • Meyer Rémi
  • Giust Remo
  • Xie Chen
  • Morel Benoît
  • Ouadghiri Idrissi Ismail
  • Furfaro Luca
  • Froehly Luc
  • Couairon Arnaud
  • Bonnaud Guy
  • Courvoisier François
  , 2022. The extreme intensity provided by ultrafast laser pulses has enabled a number of scientific and technological advances in a number of areas in photonics and material science. The laser-generated plasma can be particularly used to create Extreme UV sources, to synthetize new materials phases or, if it is dense and hot enough, it can relax into Warm Dense Matter, which is an intermediate state in-between hot plasmas and solid-state. It is still particularly challenging to study and model and is of primary importance in research on inertial confinement fusion or on the core of several astrophysics objects. Up to here, dense plasmas were generated at the surface of materials, where the expansion rapidly cools down the plasma. It would be particularly attractive to generate such warm dense matter and hot plasmas within the bulk of solid dielectrics, where the infrared laser can create a localized plasma in 3D. However, because of the beam defocusing due to the plasma generated by the onset of the pulse, only underdense plasmas could be generated inside solids- apart in the case of extreme focusing where the applicability is very limited. We demonstrate with a combination of experimental and Particle-In-Cell simulations that ultrafast Bessel beams can generate over-dense plasmas in the bulk of transparent solids. We show that collisionless resonance absorption is a primary mechanism of the absorption inside the plasma. It yields an extreme mass energy density of several MJ/kg and we estimate from our measurements that the temperature can reach 10 eV.
• Impact of azimuthal forcing on the Brillouin limit in a collisional two-species Ohkawa filter
  
  • Nicolas Timothée
  Physics of Plasmas, American Institute of Physics, 2022, 29 (4), pp.042105. This paper investigates the physics of plasma separation in a two species rotating collisional Ohkawa filter, when the source of rotation is an orbital angular momentum carrying wave. The electric field is treated self-consistently with ion and electron radial motion. The injection of angular momentum causes radial currents leading to charge penetration and electric field build up. The electric field varies until an equilibrium with the friction forces is reached. Both collisions with neutrals and Coulomb collisions are considered. In the case where the electric field is driven by the resonant wave, there is no collisional breakdown of the Brillouin limit [Rax et al., Phys. Plasmas 22, 092101 (2015)]; on the contrary, the maximum achievable electric field decreases when the collision frequency is increased. When two species are present, one that undergoes the wave forcing while the second does not interact with the wave, we find the following: the first species is confined, while the second species can be expelled or confined depending on the charge to mass ratio and the collisionalities. Assuming equal charge numbers, if the second species is the heavy one, it is always expelled, which is a standard result. When the second species is the light one, it can also be expelled in the common case where neutral collisions dominate over Coulomb collisions, which constitutes a new result. (10.1063/5.0073198)
  DOI : 10.1063/5.0073198
• Interorbital singlet pairing in Sr 2 RuO 4 : A Hund's superconductor
  
  • Käser Stefan
  • Strand Hugo
  • Wentzell Nils
  • Georges Antoine
  • Parcollet Olivier
  • Hansmann Philipp
  Physical Review B, American Physical Society, 2022, 105 (15), pp.155101. (10.1103/PhysRevB.105.155101)
  DOI : 10.1103/PhysRevB.105.155101
• Snowmass White Paper: S-matrix Bootstrap
  
  • Kruczenski Martin
  • Penedones Joao
  • van Rees Balt C.
  , 2022. The S-matrix Bootstrap originated on the idea that the S-matrix might be fully constrained by global symmetries, crossing, unitarity, and analyticity without relying on an underlying dynamical theory that may or may not be a quantum field theory. Recently this approach was revived from a somewhat different point of view. Using the same constraints, one numerically maps out the (infinite-dimensional) space of allowed S-matrices that should contain all consistent quantum field theories (and quantum theories of gravity). Moreover, in the best case scenario one finds special points in the space that can be identified with a certain quantum field theory of interest. In that case, the approach allows the numerical computation of the S-matrix without relying on the particular Lagrangian of the theory. In this white paper we summarize the state of the art and discuss the future of the topic.
• On the role of bandwidth in pump and seed light waves for stimulated Raman scattering in inhomogeneous plasmas
  
  • Luo Mufei
  • Hüller Stefan
  • Chen Min
  • Sheng Zhengming
  Physics of Plasmas, American Institute of Physics, 2022, 29, pp.032102. (10.1063/5.0078985)
  DOI : 10.1063/5.0078985
• Control of the acoustic waves generated by intense laser filamentation in water
  
  • Jukna V.
  • Albert S.
  • Millon C.
  • Mahieu Benoît
  • Guillermin R.
  • Rabau G.
  • Fattaccioli D.
  • Mysyrowicz André
  • Couairon A.
  • Houard Aurélien
  Optics Express, Optical Society of America - OSA Publishing, 2022, 30 (6), pp.9103-9111. Experiments and simulations are performed to study filamentation and generation of acoustic waves in water by loosely focused multi-millijoules laser pulses. When the laser pulse duration is increased from femtosecond to nanosecond duration, a transition is observed from a filamentary propagation with extended and low energy density deposition to a localized breakdown, related to high energy density deposition. The transition suggests that Kerr selffocusing plays a major role in the beam propagation dynamics. As a result, the shape, the amplitude and the spectrum of the resulting pressure wave present a strong dependence on the laser pulse duration. (10.1364/OE.453749)
  DOI : 10.1364/OE.453749
• Fast Principal Minor Algorithms for Quantum Many Body Systems
  
  • Šimkovic IV Fedor
  • Ferrero M.
  Physical Review B, American Physical Society, 2022, 105 (12), pp.125104. The computation of determinants plays a central role in diagrammatic Monte Carlo algorithms for strongly correlated systems. The evaluation of large numbers of determinants can often be the limiting computational factor determining the number of attainable diagrammatic expansion orders. In this work we build upon the algorithm presented in [\emph{Linear Algebra and its applications} 419.1 (2006), 107-124] which computes all principal minors of a matrix in $O(2^n)$ operations. We present multiple generalizations of the algorithm to the efficient evaluation of certain subsets of all principal minors with immediate applications to Connected Determinant Diagrammatic Monte Carlo within the normal and symmetry-broken phases as well as Continuous-time Quantum Monte Carlo. Additionally, we improve the asymptotic scaling of diagrammatic Monte Carlo formulated in real-time to $O(2^n)$ and report speedups of up to a factor $25$ at computationally realistic expansion orders. We further show that all permanent-principal-minors, corresponding to sums of bosonic Feynman diagrams, can be computed in $O(3^n)$, making diagrammatic Monte Carlo for bosonic and mixed systems a viable path worth exploring. (10.1103/PhysRevB.105.125104)
  DOI : 10.1103/PhysRevB.105.125104
• Demographic study of major conferences in heavy ion physics
  
  • Nattrass Christine
  • Andres Carlota
  • Belmont Ron
  • Blue Jennifer
  • Cochran Geraldine
  • Connors Megan
  • Frantz Justin
  • Mroczek Debora
  • Noronha-Hostler Jacquelyn
  • Nelson Stacyann
  • Reed Rosi
  • Salur Sevil
  • Sharma Natasha
  • Patrick Steffanic Patrick
  • Thomas Deepa
  • Ye Zhenyu
  , 2022, 3 (4). We present a study of the demographics of major conferences in heavy ion physics. We look at the distribution of talks by gender for Quark Matter, Strangeness in Quark Matter, Initial Stages, and Hard Probes between 2011–2022. We find that women are often underrepresented among plenary speakers and usually underrepresented among parallel speakers. At Quark Matter, women are more likely to be given a poster presentation in lieu of an oral presentation. The Quark Matter summary talk has never been given by a woman. We discuss the collection of data and possible approaches to make the field more equitable and, therefore, more scientifically productive. (10.31349/SuplRevMexFis.3.040922)
  DOI : 10.31349/SuplRevMexFis.3.040922
• Combining semilocal exchange with dynamical mean-field theory: Electronic structure and optical response of rare-earth sesquioxides
  
  • Boust James
  • Galler Anna
  • Biermann Silke
  • Pourovskii Leonid
  Physical Review B, American Physical Society, 2022, 105 (8), pp.085133. (10.1103/PhysRevB.105.085133)
  DOI : 10.1103/PhysRevB.105.085133
• The F-theorem in the melonic limit
  
  • Benedetti Dario
  • Gurau Razvan
  • Harribey Sabine
  • Lettera Davide
  Journal of High Energy Physics, Springer, 2022, 2022 (2), pp.147. The F -theorem states that in three dimensions the sphere free energy of a field theory must decrease between ultraviolet and infrared fixed points of the renormalization group flow, and it has been proven for unitary conformal field theories (CFTs). We consider here the long-range bosonic O ( N ) 3 model on a spherical background, at next-to-next-to-leading order of the 1 /N expansion. The model displays four large- N fixed points and we test and confirm the F -theorem holds in this case. This is non-trivial as one of the couplings is imaginary, and therefore the model is non-unitary at finite N . Despite this, several tests indicating that the large- N CFTs are in fact unitary have been performed: for instance all the OPE coefficients computed so far in the large- N limit are real, and the spectrum of bilinear operators is real and above unitarity bounds. Our result, namely that the F theorem holds at large N , can be viewed as further indication that such theories are unitary. As an added bonus, we show how conformal partial waves expansions in conformal field theory can be used to resum infinite classes of vacuum diagrams. Non-perturbatively, the jump in the value of the free energy has the interpretation of the inclusion at the ultraviolet fixed point of an extra non-normalizable contribution in the conformal partial wave expansion. This can be seen in perturbation theory as the reversal of the sign of an infinite class of diagrams due to the flow of a coupling constant. (10.1007/JHEP02(2022)147)
  DOI : 10.1007/JHEP02(2022)147
• Interacting systems and wormholes
  
  • Betzios P.
  • Kiritsis E.
  • Papadoulaki O.
  Journal of High Energy Physics, Springer, 2022, 2022 (2), pp.126. A bstract We consider a class of tripartite systems for which two d -dimensional QFTs are cross-coupled via a third d + 1-dimensional “messenger” QFT. We analyse in detail the example of a pair of one-dimensional matrix quantum mechanics) coupled via a two­dimensional theory of the BF-type and compute its partition function and simple correlators. This construction is extendible in higher dimensions) using a Chern-Simons “messenger” theory. In all such examples, the exact partition function acquires a form, speculated to correspond to systems dual to Euclidean wormholes and the cross correlators are sufficiently soft and consistent with analogous gravitational calculations. Another variant of the tripartite system is studied, where the messenger theory is described by a non-self-interacting (matrix)-field, reaching similar conclusions. While the Euclidean theories we consider are perfectly consistent, the two possible analytic continuations into Lorentzian signature (messenger vs. boundary QFT directions) of the tripartite models, reveal physical features and “pathologies” resembling those of the expected Lorentzian gravitational backgrounds. (10.1007/JHEP02(2022)126)
  DOI : 10.1007/JHEP02(2022)126
• Interfacial charge transfer and persistent metallicity of ultrathin SrIrO 3 /SrRuO 3 heterostructures
  
  • Nelson Jocienne
  • Schreiber Nathaniel
  • Georgescu Alexandru
  • Goodge Berit
  • Faeth Brendan
  • Parzyck Christopher
  • Zeledon Cyrus
  • Kourkoutis Lena
  • Millis Andrew
  • Georges Antoine
  • Schlom Darrell
  • Shen Kyle
  Science Advances, American Association for the Advancement of Science (AAAS), 2022, 8 (5), pp.eabj0481-1/eabj0481-8. Interface quantum materials have yielded a plethora of previously unknown phenomena, including unconventional superconductivity, topological phases, and possible Majorana fermions. Typically, such states are detected at the interface between two insulating constituents by electrical transport, but whether either material is conducting, transport techniques become insensitive to interfacial properties. To overcome these limitations, we use angle-resolved photoemission spectroscopy and molecular beam epitaxy to reveal the electronic structure, charge transfer, doping profile, and carrier effective masses in a layer-by-layer fashion for the interface between the Dirac nodal-line semimetal SrIrO 3 and the correlated metallic Weyl ferromagnet SrRuO 3 . We find that electrons are transferred from the SrIrO 3 to SrRuO 3 , with an estimated screening length of λ = 3.2 ± 0.1 Å. In addition, we find that metallicity is preserved even down to a single SrIrO 3 layer, where the dimensionality-driven metal-insulator transition typically observed in SrIrO 3 is avoided because of strong hybridization of the Ir and Ru t 2 g states. (10.1126/sciadv.abj0481)
  DOI : 10.1126/sciadv.abj0481
• Seebeck Coefficient in a Cuprate Superconductor: Particle-Hole Asymmetry in the Strange Metal Phase and Fermi Surface Transformation in the Pseudogap Phase
  
  • Gourgout A.
  • Grissonnanche G.
  • Laliberté F.
  • Ataei A.
  • Chen L.
  • Verret S.
  • Zhou J.-S.
  • Mravlje J.
  • Georges A.
  • Doiron-Leyraud N.
  • Taillefer Louis
  Physical Review X, American Physical Society, 2022, 12 (1), pp.011037-1/011037-14. We report measurements of the Seebeck effect in both the ab plane (Sa) and along the c axis (Sc) of the cuprate superconductor La1.6−xNd0.4SrxCuO4 (Nd-LSCO), performed in magnetic fields large enough to suppress superconductivity down to low temperature. We use the Seebeck coefficient as a probe of the particle-hole asymmetry of the electronic structure across the pseudogap critical doping p⋆=0.23. Outside the pseudogap phase, at p=0.24>p⋆, we observe a positive and essentially isotropic Seebeck coefficient as T→0. That S>0 at p=0.24 is at odds with expectations given the electronic band structure of Nd-LSCO above p⋆ and its known electronlike Fermi surface. We can reconcile this observation by invoking an energy-dependent scattering rate with a particle-hole asymmetry, possibly rooted in the non-Fermi-liquid nature of cuprates just above p⋆. Inside the pseudogap phase, for p<p⋆, Sa is seen to rise at low temperature as previously reported, consistent with the drop in carrier density n from n≃1+p to n≃p across p⋆ as inferred from other transport properties. In stark contrast, Sc at low temperature becomes negative below p⋆, a novel signature of the pseudogap phase. The sudden drop in Sc reveals a change in the electronic structure of Nd-LSCO upon crossing p⋆. We can exclude a profound change of the scattering across p⋆ and conclude that the change in the out-of-plane Seebeck coefficient originates from a transformation of the Fermi surface. (10.1103/PhysRevX.12.011037)
  DOI : 10.1103/PhysRevX.12.011037
• Verification and validation of linear gyrokinetic and kinetic-MHD simulations for internal kink instability in DIII-D tokamak
  
  • Brochard G.
  • Bao J.
  • Liu C.
  • Gorelenkov N.
  • Choi G.
  • Dong G.
  • Liu P.
  • Mc.Clenaghan J.
  • Nicolau J.H.
  • Wang F.
  • Wang W.H.
  • Wei X.
  • Zhang W.L.
  • Heidbrink W.
  • Graves J.P.
  • Lin Z.
  • Lütjens Hinrich
  Nuclear Fusion, IOP Publishing, 2022, 62 (3), pp.036021. Abstract Verification and linear validation of the internal kink instability in tokamak have been performed for both gyrokinetic (GTC) and kinetic-MHD codes (GAM-solver, M3D-C1-K, NOVA, XTOR-K). Using realistic magnetic geometry and plasma profiles from the same equilibrium reconstruction of the DIII-D shot #141216, these codes exhibit excellent agreement for the growth rate and mode structure of the internal kink mode when all kinetic effects are suppressed. The simulated radial mode structures, obtained from linear simulations, are in reasonable agreement with the normalised electron cyclotron emission measurement after adjusting, within the experimental uncertainty, the safety factor q = 1 flux-surface location in the equilibrium reconstruction. Compressible magnetic perturbations strongly destabilize the kink, while poloidal variations of the equilibrium current density reduce the growth rate of the kink. Furthermore, kinetic effects of thermal ions are found to decrease the kink growth rate in kinetic-MHD simulations, but increase the kink growth rate in gyrokinetic simulations, due to the additional drive of the ion temperature gradient and parallel electric field. Kinetic thermal electrons are found to have negligible effects on the internal kink instability. (10.1088/1741-4326/ac48a6)
  DOI : 10.1088/1741-4326/ac48a6
• Probing the Gluon Orbital Angular Momentum at the EIC
  
  • Bhattacharya Shohini
  • Boussarie Renaud
  • Hatta Yoshitaka
  , 2023, 16 (7), pp.1. In these proceedings, we calculate double-spin asymmetry (DSA) in exclusive dijet production in ep collisions and we demonstrate for the first time that the cos(ϕ) angular correlation between the scattered electron and proton is a simultaneous probe of the gluon orbital angular momentum and its interplay with the gluon helicity. We make a rough estimate of the DSA for the kinematics of the Electron-Ion Collider. (10.5506/aphyspolbsupp.16.7-a16)
  DOI : 10.5506/aphyspolbsupp.16.7-a16
• Trigonal-to-monoclinic structural transition in TiSe$_2$ due to a combined condensation of $\mathbf{ \textit{q} = (\frac{1}{2},0,0)}$ and $\mathbf{(\frac{1}{2},0,\frac{1}{2})}$ phonon instabilities
  
  • Subedi Alaska
  Physical Review Materials, American Physical Society, 2022. I present first principles calculations of the phonon dispersions of TiSe$_2$ in the $P\overline{3}c1$ phase, which is the currently accepted low-temperature structure of this material. They show weak instabilities in the acoustic branches in the out-of-plane direction, suggesting that this phase may not be the true ground state. To find the lowest energy structure, I study the energetics of all possible distorted structures corresponding to the isotropy subgroups of $P\overline{3}m1$ for the $M_1^-$ and $L_1^-$ phonon instabilities present in this high-temperature phase at $q = (\frac{1}{2},0,0)$ and $(\frac{1}{2},0,\frac{1}{2})$, respectively. I was able to stabilize 10 different structures that are lower in energy relative to the parent $P\overline{3}m1$ phase, including two monoclinic structures more energetically stable than the $P\overline{3}c1$ phase. The lowest energy structure has the space group $C2$ with the order parameter $M_1^- (a,0,0) + L_1^- (0,b,b)$. This structure lacks inversion symmetry, and its primitive unit cell has 12 atoms. (10.1103/PhysRevMaterials.6.01460)
  DOI : 10.1103/PhysRevMaterials.6.01460
• Hexagonal-to-base-centered-orthorhombic $4Q$ charge density wave order in kagome metals KV$_3$Sb$_5$, RbV$_3$Sb$_5$, and CsV$_3$Sb$_5$
  
  • Subedi Alaska
  Physical Review Materials, American Physical Society, 2022. I search for the ground state structures of the kagome metals KV$_3$Sb$_5$, RbV$_3$Sb$_5$, and CsV$_3$Sb$_5$ using first principles calculations. Group-theoretical analysis shows that there are seventeen different distortions that are possible due to the phonon instabilities at the $M$ $(\frac{1}{2},0,0)$ and $L$ $(\frac{1}{2},0,\frac{1}{2})$ points in the Brilouin zone of the parent $P6/mmm$ phase of these materials. I generated these structures for the three compounds and performed full structural relaxations that minimize the atomic forces and lattice stresses. I find that the $Fmmm$ phase with the order parameter $M_1^+$ $(a,0,0)$ $+$ $L_2^-$ $(0,b,b)$ has the lowest energy among these possibilities in all three compounds. However, the $Fmmm$ exhibits a dynamical instability at its $Z$ $(0,0,1)$ point, which corresponds to the $A$ $(0,0,\frac{1}{2})$ point in the parent $P6/mmm$ phase. Condensation of this instability leads to a base-centered orthorhombic structure with the space group $Cmcm$ and $4Q$ order parameter $M_1^+$ $(a,0,0)$ $+$ $L_2^-$ $(0,b,b)$ $+$ $A_6^+$ $(\frac{1}{2}c,\frac{-\sqrt{3}}{2}c)$. (10.1103/PhysRevMaterials.6.015001)
  DOI : 10.1103/PhysRevMaterials.6.015001
• Fluctuating local field approach to free energy of one-dimensional molecules with strong collective electronic fluctuations
  
  • Lyakhova Yana
  • Stepanov Evgeny
  • Rubtsov Alexey
  Physical Review B, American Physical Society, 2022, 105 (3), pp.035118. (10.1103/PhysRevB.105.035118)
  DOI : 10.1103/PhysRevB.105.035118
• Black tsunamis and naked singularities in AdS
  
  • Emparan Roberto
  • Licht David
  • Suzuki Ryotaku
  • Tomašević Marija
  • Way Benson
  Journal of High Energy Physics, Springer, 2022, 02, pp.090. We study the evolution of the Gregory-Laflamme instability for black strings in global AdS spacetime, and investigate the CFT dual of the formation of a bulk naked singularity. Using an effective theory in the large D limit, we uncover a rich variety of dynamical behaviour, depending on the thickness of the string and on initial perturbations. These include: large inflows of horizon generators from the asymptotic boundary (a ‘black tsunami’); a pinch-off of the horizon that likely reveals a naked singularity; and competition between these two behaviours, such as a nakedly singular pinch-off that subsequently gets covered by a black tsunami. The holographic dual describes different patterns of heat flow due to the Hawking radiation of two black holes placed at the antipodes of a spherical universe. We also present a model that describes, in any D, the burst in the holographic stress-energy tensor when the signal from a bulk self-similar naked singularity reaches the boundary. The model shows that the shear components of the boundary stress diverge in finite time, while the energy density and pressures from the burst vanish. (10.1007/JHEP02(2022)090)
  DOI : 10.1007/JHEP02(2022)090