arXiv subjects

Ivan Maggio-Aprile

Publications and source records attributed to Ivan Maggio-Aprile.

8 recordsLinked to original sources

arXiv2025

Vortex core spectroscopy links pseudogap and Lifshitz critical point in a cuprate superconductor

Understanding how superconductivity competes with other electronic phases in cuprates requires direct access to the hidden non-superconducting low temperature phase, for which Abrikosov vortices provide a unique local probe. We map the doping- and field-dependent evolution of vortex-core states in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ across a broad doping range spanning the Fermi-surface Lifshitz transition. High-resolution scanning tunneling spectroscopy reveals a striking transformation of the vortex-core spectrum from unconventional, pseudogap-like signatures at moderate doping to more BCS-like behavior beyond a critical doping $p^* \approx 0.21$. This crossover aligns with the pseudogap endpoint and the onset of Fermi-surface reconstruction, indicating a direct link between pseudogap physics and vortex electronic structure. Our findings highlight the vortex core as a sensitive local probe of the cuprate ground state.

cond-mat.supr-con↗

arXiv2024

Feedback loop dependent charge density wave imaging by scanning tunneling spectroscopy

Scanning Tunneling Spectroscopy (STS) is a unique technique to probe the local density of states (LDOS) at the atomic scale by measuring the tunneling conductance between a sharp tip and a sample surface. However, the technique suffers of well-known limitations, the so-called set-point effect, which can potentially introduce artifacts in the measurements. We compare several STS imaging schemes applied to the LDOS modulations of the charge density wave state on atomically flat surfaces, and demonstrate that only constant-height STS is capable of mapping the intrinsic LDOS. In the constant-current STS, commonly used and easier-to-implement, the tip-sample distance variations imposed by the feedback loop result in set-point-dependent STS images and possibly mislead the identification of the CDW gap edges.

cond-mat.mtrl-sci↗

arXiv2023

Vortex-core spectroscopy of $d$-wave cuprate high-temperature superconductors

The mechanism of high-temperature superconductivity remains one of the great challenges of contemporary physics. Here, we review efforts to image the vortex lattice in copper oxide-based high-temperature superconductors and to measure the characteristic electronic structure of the vortex core of a $d$-wave superconductor using scanning tunneling spectroscopy.

cond-mat.supr-con↗

arXiv2021

Wang-MacDonald d-wave vortex cores observed in heavily overdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

Low magnetic field scanning tunneling spectroscopy of individual Abrikosov vortices in heavily overdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ unveils a clear d-wave electronic structure of the vortex core, with a zero-bias conductance peak at the vortex center that splits with increasing distance from the core. We show that previously reported unconventional electronic structures, including the low energy checkerboard charge order in the vortex halo and the absence of a zero-bias conductance peak at the vortex center, are direct consequences of short inter-vortex distance and consequent vortex-vortex interactions prevailing in earlier experiments.

cond-mat.supr-con↗

arXiv2017

Observation of Caroli-de Gennes-Matricon Vortex States in YBa$_2$Cu$_3$O$_{7-δ}$

The copper oxides present the highest superconducting temperature and properties at odds with other compounds, suggestive of a fundamentally different superconductivity. In particular, the Abrikosov vortices fail to exhibit localized states expected and observed in all clean superconductors. We have explored the possibility that the elusive vortex-core signatures are actually present but weak. Combining local tunneling measurements with large-scale theoretical modeling, we positively identify the vortex states in YBa$_2$Cu$_3$O$_{7-δ}$. We explain their spectrum and the observed variations thereof from one vortex to the next by considering the effects of nearby vortices and disorder in the vortex lattice. We argue that the superconductivity of copper oxides is conventional, but the spectroscopic signature does not look so because the superconducting carriers are a minority.

cond-mat.supr-con↗

arXiv2016

Revisiting the vortex-core tunnelling spectroscopy in YBa$_2$Cu$_3$O$_{7-δ}$

The observation by scanning tunnelling spectroscopy (STS) of Abrikosov vortex cores in the high-temperature superconductor YBa$_2$Cu$_3$O$_{7-δ}$ (Y123) has revealed a robust pair of electron-hole symmetric states at finite subgap energy. Their interpretation remains an open question because theory predicts a different signature in the vortex cores, characterised by a strong zero-bias conductance peak. We present STS data on very homogeneous Y123 at 0.4 K revealing that the subgap features do not belong to vortices: they are actually observed everywhere along the surface with high spatial and energy reproducibility, even in the absence of magnetic field. Detailed analysis and modelling show that these states remain unpaired in the superconducting phase and belong to an incoherent channel which contributes to the tunnelling signal in parallel with the superconducting density of states.

cond-mat.supr-con↗

arXiv2008

Unexpectedly wide reversible vortex region in $β$-pyrochlore RbOs$_{2}$O$_{6}$

We study the extent of the reversible region in the vortex phase diagram of recently available RbOs$_2$O$_6$ single crystals \cite{Rogacki08a} by means of bulk magnetization measurements. We found that the irreversible magnetic response sets in at a field $H_{\rm irr}(T) \sim 0.3 H_{\rm c2}(T)$ for $0.5 \lesssim T/T_{\rm c} \lesssim 0.8$, yielding a reversible vortex region that is uncommonly wide in comparison with typical low-$T_{\rm c}$ materials. The relevance of thermal fluctuations is limited since we estimate a Ginzburg number $G_{\rm i} = 5 \times 10^{-7}$. However, the relevance of quenched disorder is unconventionally low since the critical-current density ratio at low fields and temperatures is of the order of that found in high-T$_{\rm c}$'s. We therefore conclude that an intrinsically low bulk pinning magnitude favors the existence of an unexpectedly wide reversible vortex region that seems to be generic to $β$-pyrochlores.

cond-mat.supr-con↗

arXiv2006

Scanning tunneling spectroscopy of high-temperature superconductors

Tunneling spectroscopy played a central role in the experimental verification of the microscopic theory of superconductivity in the classical superconductors. Initial attempts to apply the same approach to high-temperature superconductors were hampered by various problems related to the complexity of these materials. The use of scanning tunneling microscopy/spectroscopy (STM/STS) on these compounds allowed to overcome the main difficulties. This success motivated a rapidly growing scientific community to apply this technique to high-temperature superconductors. This paper reviews the experimental highlights obtained over the last decade. We first recall the crucial efforts to gain control over the technique and to obtain reproducible results. We then discuss how the STM/STS technique has contributed to the study of some of the most unusual and remarkable properties of high-temperature superconductors: the unusual large gap values and the absence of scaling with the critical temperature; the pseudogap and its relation to superconductivity; the unprecedented small size of the vortex cores and its influence on vortex matter; the unexpected electronic properties of the vortex cores; the combination of atomic resolution and spectroscopy leading to the observation of periodic local density of states modulations in the superconducting and pseudogap states, and in the vortex cores.

cond-mat.supr-con↗