Current-voltage characteristics and vortex dynamics in highly underdoped La2−x_{2-x}Srx_{x}CuO4_{4}

The temperature dependence of the nonlinear current-voltage ($I$-$V$) characteristics in highly underdoped La$_{2-x}$Sr$_{x}$CuO$_{4}$ ($x=0.07$ and 0.08) thick films has been studied in both zero and perpendicular magnetic fields $H$. Power-law behavior of $V(I)$ is found for both $H=0$ and $H \neq 0$. The critical current $I_{c}$ was extracted, and its temperature and magnetic field dependences were studied in detail. The Berezinskii-Kosterlitz-Thouless physics dominates the nonlinear $I$-$V$ near the superconducting transition at $H=0$, and it continues to contribute up to a characteristic temperature $T_x(H)$. Nonlinear $I$-$V$ persists up to an even higher temperature $T_{h}(H)$ due to the depinning of vortices.Comment: 4 pages, 4 figures; Superstripes 2015 conferenc

Layout optimization for multi-bi-modulus materials system under multiple load cases

Financial support from the National Natural Science Foundation of China (Grant No. 51179164) and the Australian Research Council (Grant No. DP140103137) is acknowledged

Proliferation of metallic domains caused by inhomogeneous heating near the electrically-driven transition in VO2_2 nanobeams

We discuss the mechanisms behind the electrically driven insulator-metal transition in single crystalline VO$_2$ nanobeams. Our DC and AC transport measurements and the versatile harmonic analysis method employed show that non-uniform Joule heating causes phase inhomogeneities to develop within the nanobeam and is responsible for driving the transition in VO$_{2}$. A Poole-Frenkel like purely electric field induced transition is found to be absent and the role of percolation near and away from the electrically driven transition in VO$_{2}$ is also identified. The results and the harmonic analysis can be generalized to many strongly correlated materials that exhibit electrically driven transitions

Unveiling the phase diagram of a striped cuprate at high magnetic fields: hidden order of Cooper pairs

The interplay of charge orders with superconductivity in underdoped cuprates at high magnetic fields (H) is an open question, and even the value of the upper critical field (Hc2), a measure of the strength of superconductivity, has been the subject of a long-term debate. We combined three complementary transport techniques on underdoped La1.8−xEu0.2SrxCuO4 with a "striped" charge order and a low H=0 transition temperature T0c, to establish the T−H phase diagram and reveal the ground states in CuO2 planes: a superconductor, a wide regime of superconducting phase fluctuations (i.e. a vortex liquid), and a high-field normal state. The relatively high Hc2 is consistent with the opening of a superconducting gap above T0c, but only at T∼(2-3)T0c, an order of magnitude below the pseudogap temperature. Within the vortex liquid, an unanticipated, insulatinglike region, but with strong superconducting correlations, begins to emerge already at T≲T0c. The results suggest that the presence of stripes plays a crucial role in the freezing of Cooper pairs in this novel state. Our findings provide a fresh perspective on the pairing strength in underdoped cuprates, and introduce a new avenue for exploring the interplay of various orders

Signatures of a pair density wave at high magnetic fields in cuprates with charge and spin orders

In underdoped cuprates, the interplay of the pseudogap, superconductivity, and charge and spin ordering can give rise to exotic quantum states, including the pair density wave (PDW), in which the superconducting (SC) order parameter is oscillatory in space. However, the evidence for a PDW state remains inconclusive and its broader relevance to cuprate physics is an open question. To test the interlayer frustration, the crucial component of the PDW picture, we performed transport measurements on La$_{1.7}$Eu$_{0.2}$Sr$_{0.1}$CuO$_{4}$ and La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_{4}$, cuprates with "striped" spin and charge orders, in perpendicular magnetic fields ($H_\perp$), and also with an additional field applied parallel to CuO$_2$ layers ($H_\parallel$). We detected several phenomena predicted to arise from the existence of a PDW, including an enhancement of interlayer SC phase coherence with increasing $H_\parallel$. Our findings are consistent with the presence of local, PDW pairing correlations that compete with the uniform SC order at $T_{c}^{0}< T<(2-6) T_{c}^{0}$, where $T_{c}^{0}$ is the $H=0$ SC transition temperature, and become dominant at intermediate $H_\perp$ as $T\rightarrow 0$. These data also provide much-needed transport signatures of the PDW in the regime where superconductivity is destroyed by quantum phase fluctuations.Comment: This is a pre-print of an article published in Nature Communications. The final authenticated version is available online at: https://doi.org/10.1038/s41467-020-17138-