Time Reversal Symmetry Broken Electronic Phases in Thin Films of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

TL;DR

This work demonstrates robust two-dimensional superconductivity in sputter-grown BSCCO thin films and reveals a time-reversal-symmetry–broken electronic phase space structured by magnetic field. The superconducting state is preceded by weak anti-localization, evidenced by magnetoconductance analyzed with the Hikami–Larkin–Nagaoka framework and supplemented by superconducting fluctuation theories, indicating a crossover from vortex-dominated 2D SC to a normal metallic regime under TRS breaking. Across samples with varying disorder, the data show consistent BKT-like transitions in R(T) and nonlinear I–V scaling, while highly disordered films cross into a three-dimensional weak localization–dominated regime with no superconductivity. These findings establish WAL as a precursor to superconductivity in BSCCO thin films, connect BKT physics to transport in layered cuprates, and highlight the potential of large-area BSCCO films for cryogenic devices and scalable quantum transport platforms.

Abstract

High-temperature superconductors (high-Tc SCs) host a rich landscape of electronic phases encompassing the pseudogap, strange metal, superconducting, antiferromagnetic insulating, and Fermi-liquid regimes. The superconducting phase is notable for non-dissipative electronic functionality at relatively high temperatures. These phases are commonly probed in thermodynamic phase space by varying temperature or current through the sample. They can also be probed by breaking time-reversal symmetry (TRS) with an external magnetic field, which yields transition signatures distinct from those arising solely from temperature or current tuning. Here we show that electron transport in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ is primarily governed by two-dimensional superconductivity consistent with a Berezinskii-Kosterlitz-Thouless (BKT) topological phase transition, as supported by current-voltage characteristics measured under temperature variation; these measurements preserve TRS. In contrast, when an external magnetic field is applied, the superconducting state is consistently preceded by weak antilocalization (WAL), where bound vortex-antivortex pairs dissociate into a normal metallic state through an intermediate localized phase. We further establish that highly disordered films exhibit transport dominated by three-dimensional weak localization, with superconductivity entirely suppressed.

Figures (17)

• Figure 1: Crystal structure and transport measurements of BSCCO thin film: (a) Cross-sectional transmission electron microscopy (TEM) image of the BSCCO crystal, revealing atomic-scale lattice ordering (top right panel). False color optical microscope image of the Hall bar of BSCCO used for measurements (bottom right panel). Crystal structure of the 2212 phase of BSCCO generated using CrystalMaker software (left panel). (b) Schematic of the Hall bar measurement configuration. (c) Temperature-dependent resistance of the BSCCO thin film (thickness $t = 35~\mathrm{nm}$), with data fitted to amplitude fluctuation [eqn. (1)] and phase fluctuation [eqn. (2)] and linear fit as indicated in the legend. (d) Schematic representing plausible mechanisms of e-e correlations in different temperature regimes. Transport is driven by (I) bound vortex-antivortex pairs (II) isolated vortices and anti-vortices (III) electrons. (e) Current-voltage ($I-V$) characteristics measured at multiple temperatures, showing nonlinear scaling near the superconducting transition. Black lines are linear fit to the log-log plot of $I-V$ curve in the superconducting regime. (f) Extracted superfluid density $J_s^a$ versus tempertaure. The blue dashed line represents the universal BKT transition line $\frac{2T}{\pi}$, whose intersection with the $J_s^a(T)$ curve defines the BKT transition temperature $T_{\mathrm{BKT}}^a$.
• Figure 2: Magnetic field dependent characteristics: (a) Resistance as a function of temperature at various magnetic fields, as shown in the legend. (b) Critical temperature $T_c$ as a function of magnetic field, extracted from data in panel (a). (c) Contour plot of resistance $R$ as a function of magnetic field $B$ and temperature $T$. (d) Change in conductance $\Delta G = G(B) - G(0)$ plotted against magnetic field for three temperatures: (i) 30 K. (ii) 75 K, fitted using the Hikami–Larkin–Nagaoka (HLN) model for weak anti-localization (WAL), indicated by the black solid line and (iii) 95 K, with a quadratic fit represented by the black solid line. (e) Resistance versus temperature for 3 samples with varying $T_c$. Vertical dotted line represents 80 K. (f) Normalized magneto resistance for the 3 samples. Inset shows differential conductance for magnetoresistance for the sample with lowest $T_c$. Solid black line shows HLN fit indicating WAL. Sample identities are marked in the legend.
• Figure 3: Longitudinal resistance of semiconducting sample: (a) Resistance versus temperature for an additional sample exhibiting semiconducting behavior down to low temperatures, indicative of localization effects or reduced carrier density. (b) Longitudinal resistance as a function of magnetic field for the semiconducting sample, showing oscillatory magnetoresistance possibly related to magnetic or electronic fluctuations (inset).
• Figure 4: Hall resistance of the superconducting sample: (a) Hall resistance $R_{xy}$ measured as a function of out-of-plane magnetic field at various temperatures, illustrating the evolution of charge transport. (b) Temperature dependence of the Hall carrier concentration $n$, derived from Hall measurements, showing variation across the studied temperature range. Close to transition temperature $\approx$ 75 $K$ Hall carrier concentration changes sign from hole type to electron type.
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