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Register a new userPhonon induced rank-2 U(1) nematic liquid states
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Fascinating new phases of matter can emerge from strong electron interactions in solids. In recent years, a new exotic class of many-body phases, described by generalized electromagnetism of symmetric rank-2 electric and magnetic fields and immobile charge excitations dubbed fractons, has attracted wide attention. Beside interesting properties in their own right, they are also closely related to gapped fracton quantum orders, new phases of dipole-coversing systems, quantum information, and quantum gravity. However, experimental realization of the rank-2 U(1) gauge theory is still absent, and even known practical experimental routes are scarce. In this work we propose a scheme of coupled optical phonons and nematics as well as several of its concrete experimental constructions. They can realize the electrostatics sector of the rank-2 U(1) gauge theory. A great advantage of our scheme is that it requires only basic ingredients of phonon and nematic physics, hence can be applied to a wide range of nematic matters from liquid crystals to electron orbitals. We expect this work will provide crucial guidance for the realization of rank-2 U(1) and fracton states of matter on a variety of platforms.
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The generalization of the Nelson-Halperin-Young theory of 2D melting to the dynamical 2+1D quantum case is presented. The bosonic quantum crystal dualizes in superfluids or superconductors exhibiting nematic liquid crystalline orders, corresponding with bose condensates of dislocations exhibiting a dual shear Meissner-Higgs mechanism. The topologically ordered nematic phase suggested by Lammert, Toner and Rokshar finds a simple interpretation in this framework. The ordered nematic is a true quantum phase: the dynamical glide principle interferes with the effect that the phonon spectrum of the crystal re-emerges in the direction orthogonal to the director. Novel insights follow from the duality on the fundamental nature of superfluidity and superconductivity. The superfluid can be viewed as an elastic medium having lost its rigidity against shear stresses. Upon dualizing the electrically charged crystal the electromagnetic Meissner phase is recovered, showing peculiar screening current oscillations when the shear penetration depth becomes larger than the London penetration depth.
We show how U(1) lattice gauge theories display key signatures of ergodicity breaking in the presence of a random charge background. Contrary to the widely studied case of spin models, in the presence of Coulomb interactions, the spectral properties of such lattice gauge theories are very weakly affected by finite-volume effects. This allows to draw a sharp boundary for the ergodic regime, and thus the breakdown of quantum chaos for sufficiently strong gauge couplings, at the system sizes accessible via exact diagonalization. Our conclusions are independent on the value of a background topological angle, and are contrasted with a gauge theory with truncated Hilbert space, where instead we observe very strong finite-volume effects akin to those observed in spin chains.
The spin-orbit entangled (SOE) Jeff-state has been a fertile ground to study novel quantum phenomena. Contrary to the conventional weakly correlated Jeff=1/2 state of 4d and 5d transition metal compounds, the ground state of CuAl2O4 hosts a Jeff=1/2 state with a strong correlation of Coulomb U. Here, we report that surprisingly Cu2+ ions of CuAl2O4 overcome the otherwise usually strong Jahn-Teller distortion and instead stabilize the SOE state, although the cuprate has relatively small spin-orbit coupling. From the x-ray absorption spectroscopy and high-pressure x-ray diffraction studies, we obtained definite evidence of the Jeff=1/2 state with a cubic lattice at ambient pressure. We also found the pressure-induced structural transition to a compressed tetragonal lattice consisting of the spin-only S=1/2 state for pressure higher than Pc=8 GPa. This phase transition from the Mott insulating Jeff=1/2 to the S=1/2 states is a unique phenomenon and has not been reported before. Our study offers a rare example of the SOE Jeff-state under strong electron correlation and its pressure-induced transition to the S=1/2 state.
Nematic phases, breaking spontaneously rotational symmetry, provide for ubiquitously observed states of matter in both classical and quantum systems. These nematic states may be further classified by their $N$--fold rotational invariance described by cyclic groups $C_N$ in 2+1D. Starting from the space groups of underlying $2d$ crystals, we present a general classification scheme incorporating $C_N$ nematic phases that arise from dislocation-mediated melting and discuss the conventional tensor order parameters. By coupling the $O(2)$ matter fields to the $Z_N$ lattice gauge theory, an unified $O(2)/Z_N$ lattice gauge theory is constructed in order to describe all these nematic phases. This lattice gauge theory is shown to reproduce the $C_N$ nematic-isotropic liquid phase transitions and contains an additional deconfined phase. Finally, using our $O(2)/Z_N$ gauge theory framework, we discuss phase transitions between different $C_N$ nematics.
Novel electronic states resulting from entangled spin and orbital degrees of freedom are hallmarks of strongly correlated f-electron systems. A spectacular example is the so-called hidden-order phase transition in the heavy-electron metal URu2Si2, which is characterized by the huge amount of entropy lost at T_{HO}=17.5K. However, no evidence of magnetic/structural phase transition has been found below T_{HO} so far. The origin of the hidden-order phase transition has been a long-standing mystery in condensed matter physics. Here, based on a first-principles theoretical approach, we examine the complete set of multipole correlations allowed in this material. The results uncover that the hidden-order parameter is a rank-5 multipole (dotriacontapole) order with nematic E^- symmetry, which exhibits staggered pseudospin moments along the [110] direction. This naturally provides comprehensive explanations of all key features in the hidden-order phase including anisotropic magnetic excitations, nearly degenerate antiferromagnetic-ordered state, and spontaneous rotational-symmetry breaking.
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