arXiv subjects

R. Nicholls

Publications and source records attributed to R. Nicholls.

3 recordsLinked to original sources

arXiv2026

Programmable superconducting diode from nematic domain control in FeSe

The superconducting diode effect (SDE) allows polarity-dependent critical currents when time-reversal and current-inverting spatial symmetries are broken. Superconducting diodes show promise for applications, but inversion asymmetry is usually encoded in sample geometry or non-centrosymmetric crystals, rendering them static circuit elements. Here we demonstrate a programmable superconducting diode whose functionality is encoded in correlated electronic domains. We use the nematic superconductor FeSe as a platform and report a large intrinsic SDE with efficiencies up to $\eta \sim 75\%$ due to vortices interacting with nematic twin boundaries. The domain wall configuration thus encodes the SDE of the device. Through intense microsecond current pulses to quench the nematic order at rates exceeding $10^7$ K/s, we modify the domain pattern and control the polarity and strength of the SDE. These results establish a new paradigm in which superconducting circuit elements can be programmed through patterns imprinted into correlated electronic states.

cond-mat.supr-con↗

arXiv2026

Anisotropic fully-gapped superconductivity in quasi-one-dimensional Li$_{0.9}$Mo$_6$O$_{17}$

Superconductivity in quasi-one-dimensional Li$_{0.9}$Mo$_6$O$_{17}$ emerges from an exotic, non-metallic normal state that exhibits signatures of Tomonaga-Luttinger liquid behavior, emergent symmetry and excitonic order. The high upper critical field, $H_{c2}$, in Li$_{0.9}$Mo$_6$O$_{17}$ suggests that that the favored pairing state is spin-triplet in nature. Here, we report measurements of the magnetic penetration depth down to $0.08\,\mathrm{K}$ ($T/T_c \lesssim 0.04$) and the specific heat down to $0.4\,\mathrm{K}$ ($T/T_c \lesssim 0.2$), and show that they are consistent with a moderately-coupled, fully-gapped superconducting state with marked gap anisotropy and a minimum ($\Delta_{\rm min} \simeq 0.4\,k_{\mathrm{B}}T_c$) occurring over a very narrow region in $k$-space. Combined with knowledge of $H_{c2}$, these measurements support the presence of a nodeless and possibly odd-parity spin-triplet superconducting order parameter in Li$_{0.9}$Mo$_6$O$_{17}$.

cond-mat.supr-con↗

arXiv2023

Structural properties of epitaxial α-U thin films on Ti, Zr, W and Nb

Thin layers of orthorhombic uranium (α-U) have been grown onto buffered sapphire substrates by d.c. magnetron sputtering, resulting in the discovery of new epitaxial matches to Ti(00.1) and Zr(00.1) surfaces. These systems have been characterised by X-ray diffraction and reflectivity and the optimal deposition temperatures have been determined. More advanced structural characterisation of the known Nb(110) and W(110) buffered α-U systems has also been carried out, showing that past reports of the domain structures of the U layers are incomplete. The ability of this low symmetry structure to form crystalline matches across a range of crystallographic templates highlights the complexity of U metal epitaxy and points naturally toward studies of the low temperature electronic properties of α-U as a function of epitaxial strain.

cond-mat.mtrl-sci↗