arXiv subjects

Aya Batoul Tazi

Publications and source records attributed to Aya Batoul Tazi.

3 recordsLinked to original sources

arXiv2024

Quantum Noise Spectroscopy of Criticality in an Atomically Thin Magnet

Dynamic critical fluctuations in magnetic materials encode important information about magnetic ordering in the associated critical exponents. Using nitrogen-vacancy centers in diamond, we implement $T_2$ (spin-decoherence) noise magnetometry to study critical dynamics in a 2D Van der Waals magnet CrSBr. By analyzing NV decoherence on time scales approaching the characteristic correlation time $τ_c$ of critical fluctuations, we extract the critical exponent $ν$ for the correlation length. Our result deviates from the Ising prediction and highlights the role of long-range dipolar interactions in 2D CrSBr. Furthermore, analyzing the divergence of the correlation length suggests the possibility of 2D-XY criticality in CrSBr in a temperature window near $T_C$ where static magnetic domains are absent. Our work provides a first demonstration of $T_2$ noise magnetometry to quantitatively analyze critical scaling behavior in 2D materials.

cond-mat.mes-hall↗

arXiv2024

Superconducting magic-angle twisted trilayer graphene hosts competing magnetic order and moiré inhomogeneities

The microscopic mechanism of superconductivity in the magic-angle twisted graphene family, including magic-angle twisted trilayer graphene (MATTG), is poorly understood. Properties of MATTG, like Pauli limit violation, suggest unconventional superconductivity. Theoretical studies propose proximal magnetic states in the phase diagram, but direct experimental evidence is lacking. We show direct evidence for an in-plane magnetic order proximal to the superconducting state using two complementary electrical transport measurements. First, we probe the superconducting phase by using statistically significant switching events from superconducting to the dissipative state of MATTG. The system behaves like a network of Josephson junctions due to lattice relaxation-induced moiré inhomogeneity in the system. We observe non-monotonic and hysteretic responses in the switching distributions as a function of temperature and in-plane magnetic field. Second, in normal regions doped slightly away from the superconducting regime, we observe hysteresis in magnetoresistance with an in-plane magnetic field; showing evidence for in-plane magnetic order that vanishes $\sim$900 mK. Additionally, we show a broadened Berezinskii-Kosterlitz-Thouless transition due to relaxation-induced moiré inhomogeneity. We find superfluid stiffness $J_{\mathrm{s}}$$\sim$0.15 K with strong temperature dependence. Theoretically, the magnetic and superconducting order arising from the magnetic order's fluctuations have been proposed - we show direct evidence for both. Our observation that the hysteretic magnetoresistance is sensitive to the in-plane field may constrain possible intervalley-coherent magnetic orders and the resulting superconductivity that arises from its fluctuations.

cond-mat.mes-hall↗

arXiv2024

Stoner instabilities and Ising excitonic states in twisted transition metal dichalcogenides

Moiré transition metal dichalcogenide (TMD) systems provide a tunable platform for studying electron-correlation driven quantum phases. Such phases have so far been found at rational fillings of the moiré superlattice, and it is believed that lattice commensurability plays a key role in their stability. In this work, we show via magnetotransport measurements on twisted WSe2 that new correlated electronic phases can exist away from commensurability. The first phase is an antiferromagnetic metal that is driven by proximity to the van Hove singularity. The second is a re-entrant magnetic field-driven insulator. This insulator is formed from a small and equal density of electrons and holes with opposite spin projections - an Ising excitonic insulator.

cond-mat.str-el↗