Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session D64: Quantum Phase TransitionsRecordings Available

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Sponsoring Units: DCMP Chair: Ian Hayes, University of Maryland Room: Hyatt Regency Hotel Grant Park B 
Monday, March 14, 2022 3:00PM  3:12PM 
D64.00001: Phases and phase transitions of a disordered quantum clock model Gaurav R Khairnar, P. K. Vishnu, Ambuj Jain, Pranay M Patil, Rajesh Narayanan, Thomas Vojta We investigate the effects of quenched randomness on the phase diagram and the phase transitions of the quantum clock model. To this end, we map the model onto a (1+1)dimensional classical spin Hamiltonian with correlated disorder which we study by means of largescale MonteCarlo simulations. For weak randomness, the model features an emerging quasilongrange ordered XY phase that separates the symmetrybroken longrange ordered phase from the disordered phase. With increasing randomness, the XY phase shrinks and vanishes in a tricritical point. Along all phase boundaries, we characterize the critical behaviors and relate them to the Harris Criterion, strongdisorder renormalization group predictions [1], as well as the properties of disorderd rotor Hamiltonians [2]. 
Monday, March 14, 2022 3:12PM  3:24PM 
D64.00002: SpinPhonon Resonances in Nearly Polar Metals with SpinOrbit Coupling Abhishek Kumar, Premala Chandra, Pavel A Volkov In metals in the vicinity of a polar transition, interactions between electrons and soft phonon modes remain to be determined. Here we explore the consequences of spinorbit assisted electronphonon coupling on the collective modes of such nearly polar metals in the presense of magnetic field. We find that the soft polar phonon hybridizes with spinflip electronic excitations of the Zeemansplit bands leading to an anticrossing. The associated energy splitting allows for an unambiguous determination of the strength of the spinorbit mediated coupling to soft modes in polar metals by spectroscopic experiments. The approach to the polar transition is reflected by the softening of the effective gfactor of the hybridized spinflip mode. Analyzing the static limit, we find that the polar order parameter can be oriented by magnetic field. This provides possibilities for new switching protocols in polar metallic materials. We demonstrate that the effects we predict can be observed with current experimental techniques and discuss promising material candidates. 
Monday, March 14, 2022 3:24PM  3:36PM 
D64.00003: Quantum electrodynamics of a dissipative phase transition in a Josephson junction Roman Kuzmin, Nitish Mehta, Nicholas Grabon, Amir Burshtein, Moshe Goldstein, Vladimir Manucharyan It is conventional to rely on dc resistance and its scaling with temperature when assigning a system into the class of superconductor or insulator. However, for a Josephson junction in an ohmic environment, the conventional approach has failed to produce a definite answer. As a result, the existence of a dissipative phase transition between the superconducting and the insulating behavior of a Josephson junction remains controversial. Here, instead of measuring the junction's resistance, we study how the junction elastically and inelastically scatters the environmental photons. Instead of ohmic resistance, our environment is a Josephson transmission line with a nondissipative wave impedance, the value of which we can tune. We probe the system at the single photon level and measure the junction's reflection coefficient at frequencies exceeding the temperature. Finally, we could follow the scaling of the reflection coefficient by tuning the probe's frequency, which is more reliable than the temperature. Our approach allows us to separate the superconducting and the insulating behavior of a Josephson junction. As the environment's impedance goes up, the junction looks more and more like a capacitor to the reflecting photons, revealing the junction's insulating nature. 
Monday, March 14, 2022 3:36PM  3:48PM 
D64.00004: Lattice renormalization group approach to the quantum ordered states of the onedimensional extended Hubbard model as a function of filling Lucas Desoppi, Nicolas Dupuis, Claude Bourbonnais Onedimensional interacting fermionic systems are usually studied in the continuum limit, with a spectrum linearized in the vicinity of the two Fermi points. In these approaches, lattice effects are mostly discarded, despite the fact that they may qualitatively affect the phase diagram of the models under study. We have developed a formalism based on the Fermionic Functional Renormalization Group for models defined on a lattice. One loop flow equations for the coupling constants and susceptibilities in the particleparticle and particlehole channels have been derived. It is shown that lattice effects manifest themselves through the curvature of the spectrum, and through the dependence of the coupling constants on momenta. In this talk, we discuss the application of this method to the phase diagram of the onedimensional extended Hubbard model as a function of filling. In particular, the fate of the Charge Bond Ordered Wave phase and the disappearance of Umklapp processes away from halffilling are investigated. 
Monday, March 14, 2022 3:48PM  4:00PM 
D64.00005: Novel Approach to Unveil Quantum Phase Transitions Using Fidelity Map Mohamad Ali Marashli, Wing Chi YU, HO KIN TANG The study of quantum phases and quantum phase transitions (QPTs) has been one of the most active research areas in condensed matter physics. Identifying quantum phase transitions is key to understanding complex and novel properties in condensed matter such as unconventional superconductors and topological materials. Fidelity has been widely used to detect various types of QPTs in interacting manybody systems. However, several unconventional transitions remain difficult to identify with current methods. We propose a novel approach, i.e. the fidelity map, to detect QPTs with higher accuracy and sensitivity as compared to the conventional fidelity measures. Our scheme extends the fidelity concept from a singledimensional to a multidimensional quantity and uses a metaheuristic algorithm to search for the critical points that globally maximize the fidelity within each phase. The resulting "fidelity map" can capture a wide range of phase transitions accurately even in small and novel systems without prior knowledge, expanding the available toolset to study phase transitions in new quantum manybody systems. 
Monday, March 14, 2022 4:00PM  4:12PM 
D64.00006: Exotic Thermal Transitions with Spontaneous Symmetry Breaking Hanbit Oh, EunGook Moon We show that exotic thermal transitions with spontaneous symmetry breaking are hosted by thermal phases with topological orders. Our analysis is controlled by finding and perturbing the exact solutions of quantum rotor models coupled to the threedimensional toric code. We evaluate all critical exponents and find striking characteristics of the exotic transitions. Remarkably, the Ising and XY transitions have the same universality class, and the exotic transitions are more stable than the WilsonFisher classes under couplings to acoustic phonons and Fermi surfaces. Thus, topological orders characterize thermal transitions with spontaneous symmetry breaking in sharp contrast to the conventional wisdom stating that order parameter symmetry and spatial dimension sorely determine the universality classes of thermal transitions. Applying our results to experiments in strongly correlated systems, we provide a plausible scenario in puzzlings of doped RbFe$_2$As$_2$. 
Monday, March 14, 2022 4:12PM  4:24PM 
D64.00007: Steadystate solution for onedimensionalopenquantum systems Tharnier P Oliveira, Stefano Chesi, Stefan Kirchner, Pedro Ribeiro The generalization of quantum phase transitions into nonequilibrium conditions raises several questions. In particular, how to classify the outofequilibrium critical phenomena into universality classes, in analogy with thermal equilibrium? 
Monday, March 14, 2022 4:24PM  4:36PM 
D64.00008: Chiral symmetry breaking through spontaneous dimerization in kagom\'e metals Kitinan Pongsangangan, Riccardo Ciola, Ronny Thomale, Lars Fritz Due to an uprise in the variety of candidate compounds, kagome metals have recently gained significant attention. Among other features, kagome metals host Dirac cones as a key band structure feature away from half filling, and potentially yield an exceptionally large fine structure, beyond values found in other 2D Dirac materials such as graphene. We investigate the possibility of chiral symmetry breaking in kagome metals. Based on a heuristic lattice model, we determine the critical coupling strength and the ordering pattern by means of a SchwingerDyson meanfield analysis. As the leading instability we identify a dimerization pattern which spontaneously opens an excitation gap at the Dirac point and breaks the chiral symmetry. 
Monday, March 14, 2022 4:36PM  4:48PM 
D64.00009: Ferroelectric quantum phase transitions and polar elasticity Dan Scott, Stephen E Rowley Ferroelectrics tuned to the neighbourhood of zero temperature phase transitions present an unexpected and novel form of criticality due to the quantum fluctuations of electrical dipole fields. For displacive materials crystalizing in three spatial dimensions with multiaxial orderparameters, these fluctuations appear to exist in an effective fourdimensional space leading to nonclassical temperature dependences of the electrical susceptibility and thermal expansion. The coupling of the polarization and strain fields leads to a quantum polarelastic regime characterized by a lowtemperature peak in the susceptibility in paraelectrics near to ferroelectric quantum critical points. We present experimental and theoretical results of the electrical susceptibility and Grüneissen ratio and explore the phase diagram of KTaO3 and SrTiO3 using pressure and uniaxial stress tuning. At temperatures well below the peak, we discuss evidence for the emergence of a liquid of polarization textures exhibiting slow dynamics and a departure from the standard model of ferroelectric quantum criticality. An investigation of the insulating 'vacuum' state is likely to aid our understanding of forms of unconventional superconductivity as recently detected in electrondoped bulk and interface quantum ferroelectrics. 
Monday, March 14, 2022 4:48PM  5:00PM 
D64.00010: Deconfined criticality and bosonization duality in easyplane ChernSimons twodimensional antiferromagnets Vira Shyta Twodimensional quantum systems with competing orders can feature a deconfined quantum critical point, yielding a continuous phase transition that is incompatible with the LandauGinzburgWilson (LGW) scenario, predicting instead a firstorder phase transition. This is caused by the LGW order parameter breaking up into new elementary excitations at the critical point. Canonical candidates for deconfined quantum criticality are quantum antiferromagnets with competing magnetic orders, captured by the easyplane CP^{1} model. A delicate issue however is that numerics indicate the easyplane CP^{1} antiferromagnet to exhibit a firstorder transition. We will explore the intricate critical behavior of this model through the particlevortex duality and demonstrate an overlooked critical regime in the dual model. Furthermore, we will show that an additional topological ChernSimons term in the action changes this picture completely in several ways. We will find that the topological easyplane antiferromagnet undergoes a secondorder transition with quantized critical exponents. Moreover, a particlevortex duality naturally maps the partition function of the ChernSimons easyplane antiferromagnet into one of massless Dirac fermions. 
Monday, March 14, 2022 5:00PM  5:12PM 
D64.00011: NonHermitian quantum gases: a platform for imaginary time crystals Rodrigo Arouca, Eduardo Cantera Marino, Cristiane Morais Smith One of the most important applications of quantum mechanics is the thermodynamic description of quantum gases. Despite the fundamental importance of this topic, a comprehensive description of the thermodynamic properties of nonHermitian quantum gases is still lacking. Here, we investigate the properties of bosonic and fermionic nonHermitian systems at finite temperatures. We show that nonHermitian systems exhibit oscillations both in temperature and imaginary time. As such, they can be a possible platform to realize an imaginary time crystal (iTC) phase. The HatanoNelson model is identified as a simple lattice model to reveal this effect. In addition, we show that the conditions for the iTC to be manifest are the same as the conditions for the presence of disorder points, where the correlation functions show oscillating behavior. This analysis makes clear that our realization of iTC is effectively a way to filter one specific Matsubara mode. In this realization, the Matsubara frequency, which enters as a mathematical tool to compute correlation functions for finite temperatures, can be measured experimentally. 
Monday, March 14, 2022 5:12PM  5:24PM 
D64.00012: Exploring a link between time crystals and manybody scars in longrange interacting systems Kieran Bull, Andrew Hallam, Zlatko Papic, Ivar Martin Time crystal is a nonequilibrium state of matter which spontaneously breaks time translation symmetry. While the existence of time crystals has been theoretically and experimentally established in periodically driven systems, resulting in a spontaneous breaking of a discrete $\mathbb{Z}_2$ symmetry, here we investigate the possibility of a \emph{continuous} time crystal, which has been proposed to occur in undriven, energyconserving systems exhibiting prethermalization. Such systems are characterized by an exponentially long regime where thermalization is delayed, allowing the system to order and display longlived oscillations of its order parameter, with the frequency set by the chemical potential. On the other hand, persistent oscillations have also recently been shown to arise due to a seemingly distinct mechanism of quantum manybody scarring: the emergence of a subspace of nonthermalizing eigenstates forming an su(2) algebra representation. In this paper we investigate a possible link between these two nonequilibrium phenomena in a realistic onedimensional spin1/2 model with longrange interactions. We identify a broad parameter regime with a weakly broken SU(2) symmetry, where the model hosts quantum manybody scars. On the other hand, our extensive numerical study did not find conclusive evidence of a time crystal phase, expected to arise for sufficiently longrange interactions. We relate the difficulty of observing a continuous time crystal to a lack of separation between the prethermalization and full thermalization time scales, found to be surprisingly insensitive to variation of the parameters of the model. 
Monday, March 14, 2022 5:24PM  5:36PM 
D64.00013: Continuous transition between an ordered Ising magnet and a topological phase Shankar Ganesh, ChienHung Lin, Joseph Maciejko We propose a theory of phase transitions between symmetry breaking and (intrinsic) topological phases in twodimensional Ising spin systems. This is done by means of a parton decomposition of the Ising spins into 2N Majorana fermions, which are assumed at the meanfield level to form a Class D topological superconductor with Chern number C. Various phases are obtained by tuning C. For example, transitions between C=0,1,2 phases are described by a parton theory of massive Majorana fields coupled to an internal SO(2N) gauge field with a ChernSimons term. Utilising various levelrank dualities of ChernSimonsmatter theories, and instanton resummation methods originally developed by 't Hooft in the solution of the U(1) problem in QCD, we demonstrate phase transitions between paramagnetic, magnetically ordered, and quantum spin liquid phases for the physical Ising spins. 
Monday, March 14, 2022 5:36PM  5:48PM 
D64.00014: Quantum criticality in Ladoped CeIn Eundeok Mun, Suyoung Kim, Harim Jang, SoonGil Jung, Sangyun Lee, Soonbeom Seo, SungIl Kim, Cheol Kim, ChanKoo Park, Hanoh Lee, Tuson Park Applying pressure to CeIn_{3} suppresses the antiferromagnetic ordering (T_{N}) to zero temperature and induces a magnetic to paramagnetic transition at a critical pressure 2.65 GPa. However, the nature of quantum criticality in CeIn_{3} is still under debate, where both conventional and unconventional critical states are observed from various physical property measurements. Here we report experiments of Ce_{1x}La_{x}In_{3} system under pressure. The pressure evolution of T_{N} in Ce_{1x}La_{x}In_{3 }series is similar to that of CeIn_{3}. For 50% La substitution, T_{N} of 4 K decreases with pressure and was completely suppressed at 1.31 GPa, where the nonfermi liquid behavior is observed. Interestingly, electrical resistivity and Hall coefficient measurements as a function of doping and pressure suggest that felectrons in Ce_{1x}La_{x}In_{3} are delocalized before the system reaches the quantum critical point (QCP). [1] In this talk, the origin of the local maximum in Hall coefficient and the itinerant character of felectrons beyond the QCP will be discussed comparatively for pure and Ladiluted CeIn_{3}. 
Monday, March 14, 2022 5:48PM  6:00PM 
D64.00015: Square lattice plaquette valence bond solid (pVBS) phase in SU(N) designer Hamiltonian with twocolumn representation Souvik Kundu, Nisheeta Desai, Kedar Damle We construct an SU(N) symmetric designer fourspin Hamiltonian with a twocolumn representation and find that it realizes a plaquette valence bond solid (pVBS) phase on the square lattice for N ≥ 3. We add to this interaction the SU(N) Heisenberg interaction with a twocolumn representation which is known to realize the Néel phase for N ≤ 9 and the Haldane Nematic phase otherwise. We study the phase diagram of this model as a function of the relative strengths of the two interactions as well as the value of N. We establish direct transitions from the Néel and Haldane Nematic phases into the pVBS phase on increasing the strength of the plaquette interaction for small and large N respectively. We determine the nature of the two transitions to be first order. 
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