arXiv subjects

Vahan Nikoghosyan

Publications and source records attributed to Vahan Nikoghosyan.

6 recordsLinked to original sources

arXiv2026

On the Detection of Curl-Free Gauge Fields

In quantum theory, electromagnetic gauge fields enter directly into the phase evolution of the wavefunction and can even influence quantum systems in regions where the associated electric and magnetic fields vanish. The Aharonov-Bohm effect demonstrates that such gauge fields produce observable consequences when a coherent quantum system encloses magnetic flux along a doubly connected path. This has led to the widespread view that curl-free gauge fields are undetectable in simply connected systems, giving rise to a form of topological blindness. Here we show that this conclusion is not fundamental. During nonequilibrium processes, collective quantum systems can develop transient responses to curl-free gauge fields without enclosing magnetic flux in a static geometry. Using superconducting condensates as a concrete example, we demonstrate that the evolving phase of the macroscopic wavefunction generates supercurrents and voltage pulses whose time integral is proportional to the open-path line integral of the vector potential. In contrast to the conventional Aharonov-Bohm effect, the resulting response is not restricted modulo the flux quantum and may greatly exceed the scale associated with static doubly connected geometries. The mechanism can be interpreted as a dynamical closure of the gauge contour in spacetime and is supported by gauge-invariant arguments, time-dependent Ginzburg-Landau theory modeling, and numerical simulations. These results establish a general principle for detecting curl-free gauge fields and suggest new approaches for probing hidden gauge structures in quantum matter and beyond.

cond-mat.supr-con↗

arXiv2026

Revisiting apparent ideal diamagnetism at ambient conditions in graphene-n-heptane-permalloy systems

We previously reported apparent ideal diamagnetism at ambient conditions in a graphene-n-heptane-permalloy system. At the same time, the experiments revealed inconsistent behavior, including signal freezing and occasional paramagnetic responses. Further measurements performed without graphene produced similar signals, indicating that graphene is not responsible for the observed effects. The results suggest that magnetic field redistribution caused by inhomogeneities in the permalloy foil and experimental geometry can mimic ideal diamagnetism in sub-milligauss measurements. These findings revise the interpretation of our earlier results and emphasize caution in interpreting ultra-low-field magnetic measurements.

cond-mat.supr-con↗

arXiv2026

Glassy magnetic freezing of interacting clusters in LK-99-family materials

We report reproducible magnetization anomalies appearing below room temperature in copper-doped apatite materials belonging to the LK-99 family synthesized via hydrothermal methods. These anomalies are observed consistently across samples prepared under comparable conditions. Although the extracted Mydosh parameter lies within the range often associated with vortex-glass behavior in superconductors, a detailed analysis of DC magnetization, AC susceptibility, field dependence, and magnetic memory effects demonstrates that the observed phenomena are not related to superconductivity. Instead, the data are consistent with glassy magnetic freezing of interacting clusters. Compositional and structural analysis identifies covellite (CuS), an ubiquitous secondary phase in these intrinsically multiphase materials, as the primary origin of the observed behavior. Our results clarify the magnetic origin of LK-99-related anomalies and highlight the importance of phase complexity in interpreting apparent superconducting signatures in this materials family.

cond-mat.supr-con↗

arXiv2026

Diode Effect May Assist Finding Proper Superconductivity Mechanism in Copper Oxides

We present measurements demonstrating that copper-oxide high-temperature superconductors can exhibit broken time-reversal symmetry in the absence of external magnetic fields. Using $Tl_{2}Ba_{2}CaCu_{2}O_{8}$ microbridges, we observe a pronounced superconducting diode effect at 100 K under strictly zero-field conditions. This nonreciprocal response remains unchanged in magnetic fields up to $\pm 100 Oe$. Our results are consistent with recent reports of zero-field diode behavior in $Bi_{2}Sr_{2}CaCu_{2}O_{8+δ }$ and together indicate that time-reversal symmetry breaking may be an intrinsic property of the cuprate superconducting state. These findings significantly constrain theoretical models of high-temperature superconductivity that rely on time-reversal-symmetric mechanisms.

cond-mat.supr-con↗

arXiv2020

Terahertz spectroscopy evidence of possible 40 K superconductivity in rhenium-doped strontium ruthenates

Strontium ruthenates have many similarities with copper oxide superconductors and are of particular interest for the investigation of the mechanisms and conditions which lead to high-temperature superconductivity. We report here on multiple experimental indications of superconductivity with onset at 40 K in strontium ruthenate doped by rhenium and selenium with chlorine used as the flux. The main experimental evidence arises from terahertz spectroscopy of this material followed by AC and DC magnetization, as well as measurements of its heat capacity and magnetoresistance. Structural and morphological studies revealed the heterophase nature of this polycrystalline material as well as the changes of lattice parameters relative to the original phases. Experimental data show a higher critical temperature on the surface compared to that of the bulk of the sample.

cond-mat.supr-con↗

arXiv2011

Indication of Meissner Effect in Sulfur-Substituted Strontium Ruthenates

Ceramic samples of Sr2RuO(4-y)Sy (y=0.03-1.2) with intended isovalent substitution of oxygen by sulfur have been synthesized and explored in the temperature range 4-300K. It is found that at a range of optimum sulfur substitution the magnetic response of ceramic samples reveals large diamagnetic signal with amplitudes approaching comparability with that of the YBCO-superconductors. Contrary to a pure ceramic Sr2RuO4, if properly optimized, the resistivity of sulfur-substituted samples has a metallic behavior except at lower temperatures where an upturn occurs. Both synthesis conditions and results of measurements are reported. The Meissner effect may point to high-temperature superconductivity.

cond-mat.supr-con↗