arXiv subjects

Thomas Jarlborg

Publications and source records attributed to Thomas Jarlborg.

8 recordsLinked to original sources

arXiv2022

Scale free distribution of oxygen interstitials wires in optimum doped HgBa$_2$CuO$_{4+y}$

Novel nanoscale probes are opening new venues for understanding unconventional electronic and magnetic functionalities driven by multiscale lattice complexity in doped high temperature superconducting perovskites. In this work we focus on the multiscale texture at supramolecular level of atomic oxygen interstitials (O-i) stripes in HgBa$_2$CuO$_{4+y}$ at optimal doping for the highest superconducting critical temperature $T_C$=94K. We report compelling evidence for the nematic phase of oxygen-interstitial O-i atomic wires with fractal-like spatial distribution over multiple scales by using scanning micro and nano X-ray-diffraction. The scale free distribution of O-i atomic wires at optimum doping extending from micron scale down to nanoscale has been associated with the intricate filamentary network of hole rich metallic wires in the CuO$_2$ plane. The observed critical opalescence provides evidence for the proximity to a critical point controlling the emergence of high temperature superconductivity at optimum doping

cond-mat.supr-con↗

arXiv2018

Multiple electronic components and Lifshitz transitions by oxygen wires formation in layered cuprates and nickelates

There is a growing compelling experimental evidence that a quantum complex matter scenario made of multiple electronic components, and competing quantum phases is needed to grab the key physics of high critical temperature (Tc) superconductivity in layered cuprates. While it is known that defects self-organization controls Tc, the mechanism remains an open issue. Here we focus on the theoretical prediction of the multi-band electronic structure and the formation of broken Fermi surfaces generated by the self-organization of oxygen interstitials O-i atomic wires in the spacer layers in HgBa2CuO4+y, La2CuO4+y and La2NiO4+y, by means of self-consistent Linear Muffin-Tin Orbital (LMTO) calculations. The electronic structure of a first phase of ordered O-i atomic wires and of a second glassy phase made of disordered O-i impurities have been studied through supercell calculations. We show the common features of the influence of O-i wires in the electronic structure in three type of materials. The ordering of O-i into wires lead to a separation of the electronic states between the O-i ensemble and the rest of the bulk. The wires formation produce first quantum confined localized states near the wire which coexist with second delocalized states in the Fermi-surface (FS) of doped cuprates. In this new scenario for high Tc superconductivity, Kitaev wires with Majorana bound states are proximity-coupled to a 2D d-wave superconductor in cuprates.

cond-mat.supr-con↗

arXiv2017

Electronic structure of HgBa$_2$CuO$_{4+δ}$ with self-organized interstitial oxygen wires in the Hg spacer planes

While recent experiments have found that at optimum doping for the highest critical temperature in HgBa$_2$CuO$_{4+y}$ (Hg1201) the oxygen interstitials (O-i) are not homogeneously distributed but form one-dimensional atomic wires, there are no available information of its electronic structure considering self-organized O-i atomic wires. Here we report the calculated electronic structure of HgBa$_2$CuO$_{4+y}$ where oxygen interstitials form atomic wires along (1,0,0) crystal direction in the Hg layer. We find that at optimum doping for superconductivity the chemical potential is tuned near an electronic topological Lifshitz transition for the appearing of a second quasi 1D Fermi surface. A $first$ large Fermi surface coexists with a $second$ incipient quasi one dimensional (1D) Fermi surface related with atomic wires of oxygen interstitials. Increasing oxygen doping the chemical potential is driven to the band edge of the $second$ 1D-band giving a peak in the density-of-states. The new 1D electronic states are confined near the oxygen interstitial wires with a small spread only on nearby sites. Spin-polarized calculations show that the magnetic response is confined in the oxygen-poor domains free of oxygen interstitials wires and it is quite insensitive to the density of O-i wires.

cond-mat.supr-con↗

arXiv2016

Breakdown of the Migdal approximation at Lifshitz transitions with giant zero-point motion in H3S superconductor

While 203 K high temperature superconductivity in H3S has been interpreted by BCS theory in the dirty limit here we focus on the effects of hydrogen zero-point-motion and the multiband electronic structure relevant for multigap superconductivity near Lifshitz transitions. We describe how the topology of the Fermi surfaces evolves with pressure giving different Lifshitz-transitions. A neck-disrupting Lifshitz-transition (type 2) occurs where the van Hove singularity, vHs, crosses the chemical potential at 210 GPa and new small 2D Fermi surface portions appear with slow Fermi velocity where the Migdal-approximation becomes questionable. We show that the neglected hydrogen zero-point motion ZPM, plays a key role at Lifshitz transitions. It induces an energy shift of about 600 meV of the vHs. The other Lifshitz-transition (of type 1) for the appearing of a new Fermi surface occurs at 130 GPa where new Fermi surfaces appear at the Gamma point of the Brillouin zone here the Migdal-approximation breaks down and the zero-point-motion induces large fluctuations. The maximum Tc=203K occurs at 160 GPa where Ef/w0=1 in the small Fermi surface pocket at Gamma point. A Feshbach-like resonance between a possible BEC-BCS condensate at Gamma and the BCS condensate in different k-space spots is proposed.

cond-mat.supr-con↗

arXiv2015

Electronic structure of superoxygenated La2NiO4 domains with ordered oxygen interstitials

The electronic structure of La2NiO4+d, where additional oxygen interstitials are forming stripes along (1,1,0), are presented. Spin-polarized calculations show that ferromagnetism on Ni sites is reduced near the stripes and enhanced far from the stripes. Totally the magnetic moment becomes reduced because of oxygen interstitials. It is suggested that the oxygen interstitial concentration in oxygen rich domains in nickelates suppress magnetism and give multiband metallic domains.

cond-mat.mtrl-sci↗

arXiv2015

Superconductivity above the lowest Earth temperature in pressurized sulfur hydride

A recent experiment has shown a macroscopic quantum coherent condensate at 203 K, about 19 degrees above the coldest temperature recorded on the Earth, 184 K, in pressurized sulfur hydride. This discovery is relevant not only in material science and condensed matter but also in other fields ranging from quantum computing to quantum physics of living matter. It has given the start to a gold rush looking for other macroscopic quantum coherent condensates in hydrides at the temperature range of living matter 200<Tc<400K. We present here a review of the experimental results and the theoretical works and we discuss the Fermiology of H3S focusing on Lifshitz transitions as a function of pressure. We discuss the possible role of the shape resonance near a neck disrupting Lifshitz transition, in the Bianconi-Perali Valletta (BPV) theory, for rising the critical temperature in a multigap superconductor, as the Feshbach resonance rises the critical temperature in Fermionic ultracold gases.

cond-mat.supr-con↗

arXiv2015

Lifshitz transitions and zero point lattice fluctuations in sulfur hydride showing near room temperature superconductivity

Emerets's experiments on pressurized sulfur hydride have shown that H3S metal has the highest known superconducting critical temperature Tc=203K. The Emerets data show pressure induced changes of the isotope coefficient between 0.25 and 0.5, in disagreement with Eliashberg theory which predicts a nearly constant isotope coefficient. We assign the pressure dependent isotope coefficient to Lifshitz transitions induced by pressure and zero point lattice fluctuations. It is known that pressure could induce changes of the topology of the Fermi surface, called Lifshitz transitions, but were neglected in previous papers on the H$_3$S superconductivity issue. Here we propose that H3S is a multi-gap superconductor with a first condensate in the BCS regime (in the large Fermi surface with high Fermi energy) which coexists with a second condensates in the BCS-BEC crossover regime (located on a small Fermi surface spots with small Fermi energy) near the $Γ$ and M point. We discuss the need of Bianconi-Perali-Valletta (BPV) superconductivity theory for superconductivity in H3S. It includes both the correction of the chemical potential due to pairing and the configuration interaction between different condensates, neglected by the Eliashberg theory. Here the shape resonance in superconducting gaps, similar to Feshbach resonance in ultracold gases, gives a relevant contribution to amplify the critical temperature. Therefore this work provides some key tools needed in the search for new room temperature superconductors.

cond-mat.supr-con↗

arXiv2013

Fermi surface reconstruction of superoxygenated La$_2$CuO$_{4}$ with ordered oxygen interstitials

Novel imaging methods show that the mobile dopants in optimum doped La$_2$CuO$_{4+y}$ (LCO) get self-organized, instead of randomly distributed. Rigid-band models fail because of ordering of dopants and supercell calculations are required to obtain the Fermi surface reconstruction. We have performed advanced band calculations for a large supercell La$_{16}$Cu$_8$O$_{32+N}$ where $N$=1 or 2 oxygen interstitials form rows in the spacer La$_{16}$O$_{16+N}$ layers intercalated between the CuO$_2$ layers as determined by scanning nano x-ray diffraction. The additional oc cupied states made by interstitial oxygen orbitals sit well below the Fermi level ($E_F$) and lead to hole doping as expect ed. The unexpected results show that in the heavily doped puddles the altered Cu(3d)-O(2p) band hybridization at $E_F$ indu ces a multiband electronic structure with the formation of multiple Fermi surface spots: a) small gaps appear in the folde d Fermi surface, b) three mini-bands cross $E_F$ with reduced Fermi energies of 60, 150, and 240 meV respectively, c) the d ensity-of-states and band mass at $E_F$ show substantial increases, and d) spin-polarized calculations show a moderate incr ease of antiferromagnetic spin fluctuations. All calculated features are favorable to enhance superconductivity however the comparison with experimental methods probing the average electronic structure of cuprates will require the description of the electronics of a network of multigap superconducting puddles.

cond-mat.supr-con↗