Strongly correlated electrons; heavy fermions; frustrated magnetism; topological / Dirac / Weyl / nodal-line semimetals; quantum spin liquids; flat-band moire; Mott transition; axion insulators; Kondo / RKKY / DMFT.
Quantum Materials
Quantum materials overview
Materials whose properties cannot be described by single-particle band-theory; emergent phenomena from electron correlation, geometric…
Strongly correlated electrons
U / W ratio (Hubbard-U vs bandwidth) above unity drives Mott physics; cuprate high-Tc, iron-pnictide, manganite-CMR all show competing…
Heavy fermion materials
f-electron CeCu6, UPt3, YbRh2Si2 show effective-mass m* up to 1000 m_e from Kondo-lattice screening; non-Fermi-liquid near quantum critical…
Frustrated magnetism
Triangular and pyrochlore lattices prevent simple antiferromagnetic order; Anderson 1973 proposed RVB resonating-valence-bond ground state;…
Topological quantum materials
Bi2Se3 / Bi2Te3 first 3D topological insulators (Hsieh-Hasan 2008); SnTe topological-crystalline; SmB6 Kondo-topological; ZrTe5 / TaAs…
Axion insulator
MnBi2Te4 magnetic topological insulator hosts axion electrodynamics; theta = pi quantized magnetoelectric coupling; signature topological…
Dirac semimetal
Cd3As2, Na3Bi host 3D Dirac fermions (Liu 2014, Wang 2013) protected by crystal symmetry; doubly-degenerate Dirac point splits into Weyl…
Weyl semimetal (band-structure)
TaAs / NbAs / NbP / TaP host Weyl points (Xu 2015 / Lv 2015) where conduction-valence bands touch linearly with definite chirality;…
Quantum spin liquid
No symmetry breaking even at T near 0; long-range entanglement; fractional quasiparticles (spinons / visons); herbertsmithite kagome and…
Kitaev quantum spin liquid
Kitaev 2006 honeycomb-model exactly solvable; bond-dependent Ising interactions yield Majorana fermions; alpha-RuCl3 + Na2IrO3 candidates…
Flat-band moire (twisted graphene)
Cao-Jarillo-Herrero 2018: twisted bilayer graphene at 1.1 deg magic angle shows flat-bands and superconductivity / correlated insulator at…
Mott transition
Half-filled Hubbard model at U/t above 8 to 10 transitions from metal to insulator; LiV2O4, V2O3, NiS2-xSex bandwidth-tuned Mott; DMFT…
Kondo effect (resistance minimum)
Kondo 1964: dilute magnetic impurities in non-magnetic host metals produce a logarithmic resistance-minimum at low T; rho ~ a + b T^2 + c…
RKKY interaction (Ruderman-Kittel-Kasuya-Yosida)
RKKY 1954-1957: indirect exchange between localized magnetic moments mediated by conduction-electron Friedel oscillations; oscillating +…
Topological magnon
Magnon analog of topological-insulator: bosonic excitations with non-trivial Berry curvature; observed in honeycomb-lattice ferromagnets…
Hofstadter butterfly (energy spectrum)
Hofstadter 1976: 2D electron in periodic potential + magnetic field shows fractal energy spectrum vs flux-per-plaquette phi/phi_0 (rational…
Quantum spin Hall (BHZ model)
Bernevig-Hughes-Zhang 2006: HgTe/CdTe quantum-well predicted to host helical edge states; Konig 2007 confirmed Z_2 topological invariant;…
Majorana fermion (condensed matter)
Kitaev 2001 toy-model: 1D p-wave superconductor hosts unpaired Majorana zero-modes at chain ends; non-Abelian braiding statistics for…