Nigel R. Cooper
University of Cambridge
Magnetic fieldQuantum tunnellingPhysicsTopologyLattice (order)VortexQuantum spin Hall effectElectronAtomic physicsQuantum Hall effectSuperfluidityCondensed matter physicsQuantum electrodynamicsBose–Einstein condensateLandau quantizationFermionQuantum mechanicsBosonQuantumFermi gas
Publications 201
Using a widefield pump-probe microscope (with ~10 nm spatial precision and ~10 fs time resolution) we probe the temperature and fluence dependent dynamics of the collective modes in excitonic insulator candidate Ta2NiSe5. We pump with a broadband pulse centered around 500 nm and probe ~800 nm using a bandpass filter.
Moire excitons promise a new platform with which to generate and manipulate hybrid quantum phases of light and matter in unprecedented regimes of interaction strength. We explore the properties in this regime, through studies of a Bose-Hubbard model of excitons coupled to cavity photons. We show that the steady states exhibit a rich phase diagram with pronounced bi-stabilities governed by multi-photon resonances reflecting the strong inter-exciton interactions. In the presence of an incoherent p...
#1Jinyi ZhangH-Index: 7
#2Christoph EigenH-Index: 7
Last. Nir NavonH-Index: 21
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Data supporting the publication: The data presented in each figure is provided as well as all of the raw time traces of the center-of-mass velocity. The ‘Fig’ folders contain text files with the data shown in each figure, with file names providing driving amplitude and frequency identifiers. The 'CoMvData' folder contains all traces of center-of-mass velocity versus time which have been used in the paper.
1 CitationsSource
#1Hope M. Bretscher (University of Cambridge)H-Index: 5
#2Paolo Andrich (University of Cambridge)H-Index: 7
Last. Andrew J. Millis (Columbia University)H-Index: 95
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Excitonic insulators host a condensate of electron-hole pairs at equilibrium, giving rise to collective many-body effects. Although several materials have emerged as excitonic insulator candidates, evidence of long-range coherence is lacking and the origin of the ordered phase in these systems remains controversial. Here, using ultrafast pump-probe microscopy, we investigate the possible excitonic insulator Ta2NiSe5. Below 328 K, we observe the anomalous micrometer-scale propagation of coherent ...
3 CitationsSource
We demonstrate that electrostatic interactions between helical electrons at the edge of a quantum spin Hall insulator and a dynamical impurity can induce quasi-elastic backscattering. Modelling the impurity as a two-level system, we show that transitions between counterpropagating Kramers-degenerate electronic states can occur without breaking time-reversal symmetry, provided that the impurity also undergoes a transition. The associated electrical resistance has a weak temperature dependence dow...
1 CitationsSource
#1Bo SongH-Index: 6
#2Shovan DuttaH-Index: 6
Last. Ulrich SchneiderH-Index: 32
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Discontinuous quantum phase transitions and the associated metastability play central roles in diverse areas of physics ranging from ferromagnetism to false vacuum decay in the early universe. Using strongly-interacting ultracold atoms in an optical lattice, we realize a driven many-body system whose quantum phase transition can be tuned from continuous to discontinuous. Resonant shaking of a one-dimensional optical lattice hybridizes the lowest two Bloch bands, driving a novel transition from a...
#1Simon LieuH-Index: 5
#2Max McGinleyH-Index: 5
Last. Alexey V. GorshkovH-Index: 54
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Kramers' degeneracy theorem underpins many interesting effects in quantum systems with time-reversal symmetry. We show that the generator of dynamics for Markovian open fermionic systems can exhibit an analogous degeneracy, protected by a combination of time-reversal symmetry and the microreversibility property of systems at thermal equilibrium - the degeneracy is lifted if either condition is not met. We provide simple examples of this phenomenon and show that the degeneracy is reflected in the...
2 Citations
Metals composed of weakly-coupled, stacked layers possess a Fermi surface that slightly varies in size along the stacking direction. This appears in de Haas-van Alphen (dHvA) oscillations of the magnetisation with magnetic field as two close frequencies, corresponding to the two extremal Fermi surface cross-sectional areas. We show that, for layered materials of sufficiently high mobility, Coulomb interactions can have a dramatic effect on the form of the dHvA oscillations: there is also generic...