Quartic metal: Spontaneous breaking of time-reversal symmetry due to four-fermion correlations in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$

Abstract

Discoveries of ordered quantum states of matter are of great fundamental interest, and often lead to unique applications. The most well known example -- superconductivity -- is caused by the formation and condensation of pairs of electrons. A key property of superconductors is diamagnetism: magnetic fields are screened by dissipationless currents. Fundamentally, what distinguishes superconducting states from normal states is a spontaneously broken symmetry corresponding to long-range coherence of fermion pairs. Here we report a set of experimental observations in hole doped Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ which are not consistent with conventional superconducting behavior. Our specific-heat measurements indicate the formation of fermionic bound states when the temperature is lowered from the normal state. However, for $x\sim 0.8$, instead of the standard for superconductors, zero resistance and diamagnetic screening, for a range of temperatures, we observe the opposite effect: the generation of self-induced magnetic fields measured by spontaneous Nernst effect and muon spin rotation experiments. The finite resistance and the lack of any detectable diamagnetic screening in this state exclude the spontaneously broken symmetry associated with superconducting two-fermion correlations. Instead, combined evidence from transport and thermodynamic measurements indicates that the formation of fermionic bound states leads to spontaneous breaking of time-reversal symmetry above the superconducting transition temperature. These results demonstrate the existence of a broken-time-reversal-symmetry bosonic metal state. In the framework of a multiband theory, such a state is characterized by quartic correlations: the long-range order exists only for {\it pairs} of fermion pairs.

31 pages, 11 figures, supplemental information

References in corpus (19)

• Localization of preformed Cooper-pairs in disordered superconductors
• A superconductor to superfluid phase transition in liquid metallic hydrogen
• Two-Dimensional Superconducting Fluctuations in Stripe-Ordered La(1.875)Ba(0.125)CuO(4)
• Charge $4e$ superconductivity from pair density wave order in certain high temperature superconductors
• Dislocations and vortices in pair density wave superconductors
• Inter-pocket pairing and gap symmetry in Fe-based superconductors with only electron pockets
• Deconfined criticality, runaway flow in the two-component scalar electrodynamics and weak first-order superfluid-solid transitions
• Chiral CP^2 skyrmions in three-band superconductors
• Kerr effect as evidence of gyrotropic order in the cuprates
• Colossal thermomagnetic response in the exotic superconductor URu2Si2
• Unsplit superconducting and time reversal symmetry breaking transitions in Sr${}_2$RuO${}_4$ under hydrostatic pressure and disorder
• Observability of a projected new state of matter: a metallic superfluid
• Magneto-optical signatures of a cascade of transitions in La${}_2-x$Ba${}_x$CuO${}_4$
• Fermi surface reconstruction in (Ba${}_{1-x}$K${}_x$)Fe${}_2$As${}_2$ (0.44 $\le x\le$ 1) probed by thermoelectric power measurements
• Broken Time Reversal Symmetry in Superconducting Pr1-xCexPt4Ge12
• Weyl Superconductivity in UTe2
• Phase diagram of dirty two-band superconductors and observability of impurity-induced $s+is$ state
• Broken time-reversal symmetry in superconducting Pr${}_{1-x}$La${}_x$Pt${}_4$Ge${}_{12}$
• Coconuts and Islanders: A Statistics-First Guide to the Boltzmann Distribution

Cited by in corpus (55)

• Magnetic memory and spontaneous vortices in a van der Waals superconductor
• Observation of superconducting vortices carrying a temperature-dependent fraction of the flux quantum
• Cavity magnon-polaritons in cuprate parent compounds
• Spectroscopic signatures of time-reversal symmetry breaking superconductivity
• Josephson diode effects in twisted nodal superconductors
• Charge 4e superconductivity and chiral metal in the $45^{\circ }$-twisted bilayer cuprates and similar bilayers
• Supercurrent rectification with time-reversal symmetry broken multiband superconductors
• Calorimetric evidence for two phase transitions in Ba${}_{1-\mathrm{x}}$K${}_{\mathrm{x}}$Fe${}_2$As${}_2$ with fermion pairing and quadrupling states
• Prediction of time-reversal-symmetry breaking fermionic quadrupling condensate in twisted bilayer graphene
• Cooper quartet correlations in infinite symmetric nuclear matter
• Quartet Superfluid in Two-dimensional Mass-imbalanced Fermi Mixtures
• Magneto-topological transitions in multicomponent superconductors
• Multiband strong-coupling superconductors with spontaneously broken time-reversal symmetry
• Cascade of vestigial orders in two-component superconductors: nematic, ferromagnetic, s-wave charge-4e, and d-wave charge-4e states
• Observation of counterflow superfluidity in a two-component Mott insulator
• Borromean supercounterfluidity
• Demonstration of $\mathbb{C}{P}^2$ skyrmions in three-band superconductors by self-consistent solutions to a Bogoliubov-de Gennes model
• Effects of intercomponent couplings on the appearance of time-reversal symmetry breaking fermion quadrupling state in two-component London models
• Nematic Superconductivity and Its Critical Vestigial Phases in the Quasi-crystal
• Effective model and Magnetic Properties of the Resistive Electron Quadrupling State
• Vestigial singlet pairing in a fluctuating magnetic triplet superconductor: Applications to graphene moiré systems
• High-order Time-Reversal Symmetry Breaking Normal State
• Definition and Classification of Fermi Surface Anomalies
• Charge-4$e$ Superconductivity in a Hubbard model
• Biexciton-like quartet condensates in an electron-hole liquid
• Frustration driven Josephson phase dynamics
• From Fractional Quantum Anomalous Hall Smectics to Polar Smectic Metals: Nontrivial Interplay Between Electronic Liquid Crystal Order and Topological Order in Correlated Topological Flat Bands
• Pseudogap and Strong Pairing Induced by Incipient and Shallow Bands in the Quasi-Two-Dimensional KCa${}_2$Fe${}_4$As${}_4$F${}_2$
• Cooper quartets in interacting hybrid superconducting systems
• Supercurrent Diode Effect in Josephson Interferometers with Multiband Superconductors
• Stability of Bogoliubov Fermi Surfaces within BCS Theory
• The absence of Ginzburg-Landau mechanism for vestigial order in the normal phase above a two-component superconductor
• Spectra of Magnetoroton and Chiral Graviton Modes of Fractional Chern Insulator
• Evolution of dissipative regimes in atomically thin ${\text{Bi}}_2{\text{Sr}}_2{\text{CaCu}}_2{\text{O}}_{8+x}$ superconductor
• Emergent ${\mathbb{Z}}_2$ symmetry near a CDW multicritical point
• Superconducting fluctuations and charge-4$e$ plaquette state at strong coupling
• Electronic Raman response of a superconductor across a time reversal symmetry breaking phase transition
• Andreev reflection in normal metal/charge-4e superconductor junctions
• Sensing Out-of-Equilibrium and Quantum Non-Gaussian environments via induced Time-Reversal Symmetry Breaking on the quantum-probe dynamics
• Elastoresistivity of heavily hole doped 122 iron pnictides superconductors
• Microscopic theory of electron quadrupling condensates
• Ultrasound evidence for multicomponent superconducting order parameter in Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ with electron quadrupling phase
• Nematic single-component superconductivity and loop-current order from pair-density wave instability
• Microscopic properties of fractional vortices and domain walls in three-band $s+is$ superconductors
• Composite quadrupole order in ferroic and multiferroic materials
• Polar Kerr Effect in Multiband Spin-Orbit Coupled Superconductors
• Spontaneous edge corner currents in $s+is$ superconductors and time reversal symmetry breaking surface states
• Borromean supercounterfluids at finite temperatures
• Fluctuation conductivity in ultraclean multicomponent superconductors
• Revisiting vestigial order in nematic superconductors: gauge-field mechanisms and model constraints
• Hund's coupling assisted orbital-selective superconductivity in Ba1-xKxFe2As2
• Field Theory of Borromean Super-counterfluids
• Fate of Berezinskii-Kosterlitz-Thouless Paired Phase in Coupled $XY$ Models
• Topological order in higher composites
• Vortex nucleation barriers and stable fractional vortices near boundaries in multicomponent superconductors