Stefan Kirchner

The voltage-driven breakdown of a Mott insulating state is a phenomenon where both interactions and nonequilibrium effects play crucial roles. This interesting effect has generated significant theoretical and experimental interest, and may also prove technologically relevant. Recent experiments have observed a sharp nonequilibrium insulator-to-metal transition accompanied by hysteresis, negative differential conductance, and lattice deformations, but the underlying breakdown mechanism is highly debated. Here, we describe a minimal lead-driven scenario in which the breakdown can arise from voltage-induced chemical pressure and explore its ramifications for a paradigmatic model of interacting spinless fermions on a chain coupled to metallic reservoirs (leads) and calculate the charge and current responses at the RPA level. We find a complex phase diagram where the nature of the breakdown depends on the strength of the interaction, leading to various current-carrying nonequilibrium phases. For weak to intermediate interaction strengths, we identify a conducting charge-density-wave (CDW) phase with a bias-dependent ordering wave vector. At large interaction strength, the breakdown leads to a charge-separated insulating phase. Additionally, we observe instances of hysteretic behavior, sharp current onset, and negative differential conductance. Our results can help shed light on recent experimental findings and unveil a clean reference mechanism for current-induced breakdown of electronic order.

Following the rush to minerals that would enable the shift towards green economies, the Sámi homeland is quickly becoming a crucible for the rising tensions surrounding the potential for new mining projects and large-scale infrastructure projects. The roots of these conflicts date back to the colonization of the north and continue in the present with the ongoing fight to maintain the Sámi heritage, language and culture, and increasingly to gain ownership of their lands. What initially began as activism within the legal system has, on occasions, transformed into outright protests. Social media increasingly plays a key role in disseminating the message of Indigenous protest among the protesters themselves and feeding into the national and international mainstream media. This shift occurs simultaneously with the construction of a dual narrative, constituted of both land-use protest and intensified demands for Indigenous rights, including, first and foremost, the right to self-determination. Drawing from Social media theory literature and the concepts of political opportunity structures (POS) and legal opportunity structures (LOS), this study argues that social media is one of the most essential tools used by Sámi activists to raise awareness about issue-based protests as well as to communicate demands for the right to self-determination when legal and political opportunity structures are not enough to support the cause. The power of social media lies in its accessibility, immediacy and visuality, which is illustrated in the article via specific examples of mining and railway construction protests in Finland and Sweden. Social media does not replace older tools, such as international human rights litigation, but their use can complement existing strategies for defending and advancing Indigenous rights.

We investigate the effect of spin orbit coupling on proximity induced superconductivity in a normal metal attached to a superconductor. Specifically, we consider a heterostructure where the presence of interfaces gives rise to a Rashba spin orbit coupling. The properties of the induced superconductivity in these systems are addressed within the tunneling Hamiltonian formalism. We find that the spin orbit coupling induces a mixture of singlet and triplet pairing and, under specific circumstances, an odd frequency, even parity, spin triplet pairs can arise. We also address the effect of impurity scattering on the induced pairs, and discuss our results in context of heterostructures consisting of materials with spin-momentum locking.

We investigate the effect of spin-orbit coupling on proximity-induced superconductivity in a normal metal attached to a superconductor. Specifically, we consider a heterostructure where the presence of interfaces gives rise to a Rashba spin-orbit coupling. The properties of the induced superconductivity in these systems are addressed within the tunneling Hamiltonian formalism. We find that the spin-orbit coupling induces a mixture of singlet and triplet pairing and, under specific circumstances, odd-frequency, even-parity, spin-triplet pairs can arise. We also address the effect of impurity scattering on the induced pairs and discuss our results in the context of heterostructures consisting of materials with spin-momentum locking.

We report the observation of enhanced interfacial two-component superconductivity possessing a dominant triplet component in nonmagnetic CoSi₂/TiSi₂ superconductor/normal-metal planar heterojunctions.