Quantum spin liquid
[2] Quantum spin liquids generated further interest when in 1987 Anderson proposed a theory that described high-temperature superconductivity in terms of a disordered spin-liquid state.[3][4] The simplest kind of magnetic phase is a paramagnet, where each individual spin behaves independently of the rest, just like atoms in an ideal gas.These long-range patterns are referred to as "magnetic order," and are analogous to the regular crystal structure formed by many solids.Localized spins are frustrated if there exist competing exchange interactions that can not all be satisfied at the same time, leading to a large degeneracy of the system's ground state.This leads to an increase of possible orientations (six in this case) of the spins in the ground state, enhancing fluctuations and thus suppressing magnetic ordering.These states are of great theoretical interest as they are proposed to play a key role in high-temperature superconductor physics.So the equal-amplitude nearest-neighbour RVB state on square lattice is unstable and does not corresponds to a quantum spin phase.The RVB state on triangle lattice also realizes the Z2 spin liquid,[16] where different bond configurations only have real amplitudes.[26] Later theoretical work challenged this picture, arguing that all experimental results were instead consequences of 1D spinons confined to individual chains.[23] It may correspond to a gapless spin liquid with spinon Fermi surface (the so-called uniform RVB state).[19] Therefore, it is a good realization of the antiferromagnetic spin-1/2 Heisenberg model on the kagome lattice, which is a prototypical theoretical example of a quantum spin liquid.[32] A broad array of additional experiments, including 17O NMR,[33] and neutron spectroscopy of the dynamic magnetic structure factor,[34] reinforced the identification of herbertsmithite as a gapless spin liquid material, although the exact characterization remained unclear as of 2010.[37] Follow-up experiments (using 17O NMR and high-resolution, low-energy neutron scattering) refined this picture and determined there was actually a small spinon excitation gap of 0.07–0.09 meV.[44] In 2020, monodisperse single-crystal nanoparticles of herbertsmithite (~10 nm) were synthesized at room temperature, using gas-diffusion electrocrystallization, showing that their spin liquid nature persists at such small dimensions.The researchers of Oak Ridge National Laboratory, collaborating with physicists from the University of Cambridge, and the Max Planck Institute for the Physics of Complex Systems in Dresden, Germany, measured the first signatures of these fractional particles, known as Majorana fermions, in a two-dimensional material with a structure similar to graphene.[49][50] The strongly correlated quantum spin liquid (SCQSL) is a specific realization of a possible quantum spin liquid (QSL)[7][40] representing a new type of strongly correlated electrical insulator (SCI) that possesses properties of heavy fermion metals with one exception: it resists the flow of electric charge.When a magnetic field B is applied to SCI the specific heat depends strongly on B, contrary to conventional insulators.Ca10Cr7O28 is a frustrated kagome bilayer magnet, which does not develop long-range order even below 1 K, and has a diffuse spectrum of gapless excitations.[56] The experimental facts collected on heavy fermion (HF) metals and two dimensional Helium-3 demonstrate that the quasiparticle effective mass M* is very large, or even diverges.Topological fermion condensation quantum phase transition (FCQPT) preserves quasiparticles, and forms flat energy band at the Fermi level.[44] Near FCQPT, M* starts to depend on temperature T, number density x, magnetic field B and other external parameters such as pressure P, etc.The main point here is that the well-defined quasiparticles determine the thermodynamic, relaxation, scaling and transport properties of strongly correlated Fermi systems and M* becomes a function of T, x, B, P, etc.The data collected for very different strongly correlated Fermi systems demonstrate universal scaling behavior; in other words distinct materials with strongly correlated fermions unexpectedly turn out to be uniform, thus forming a new state of matter that consists of HF metals, quasicrystals, quantum spin liquid, two-dimensional Helium-3, and compounds exhibiting high-temperature superconductivity.
condensed matter physicsphase of matterquantum spinsquantum entanglementfractionalizedexcitationsPhil Andersontriangular latticeantiferromagneticallyhigh-temperature superconductivityparamagnetideal gasferromagnetantiferromagnetdomainsdisorderedferromagnetictopological orderfrustratedIsing spinsResonating valence bond theorymaximally entangledP. W. Andersonspinonstoric codemagnetic susceptibilityCurie–Weiss lawnon-analyticCurie–Weiss temperatureherbertsmithiteKagomecoupling constantmuon spin spectroscopyrhombohedralkagome latticessuperexchangeinelastic neutron scatteringspinonquantum criticalsusceptibilityantiferromagnetsheavy-fermion metalsnanoparticlesgas-diffusion electrocrystallizationYbRh2Si2Oak Ridge National LaboratoryMajorana fermionsgrapheneinsulatorheavy fermionelectric chargespecific heatheat capacitymagnetic fieldmineralkagome bilayer magnetquantum processoroptical tweezersquantum simulatorheavy fermion (HF) metalstwo dimensionalHelium-3quasiparticleeffective massTopologicalquantum phase transitionquasiparticlesenergy bandFermi leveltemperaturenumber densitypressureLandauthermodynamicrelaxationscalingtransportstate of mattermetalsquasicrystalstwo-dimensionalcompoundstopological quantum computationhigh temperature superconductivityBibcodeWolchover, NatalieQuanta MagazineWilczek, FrankCiteSeerXPhysical Review LettersPhysics ReportsNew Journal of PhysicsPhysical Review B