arXiv subjects

Thomas Meier

Publications and source records attributed to Thomas Meier.

42 records · Page 3Linked to original sources

arXiv2019

Pressure induced Hydrogen-Hydrogen interaction in metallic FeH revealed by NMR

Knowledge of the behavior of hydrogen in metal hydrides is the key for understanding their electronic properties. So far, no experimental methods exist to access these properties beyond 100 GPa, where high-Tc superconductivity emerges. Here, we present an 1H-NMR study of cubic FeH up to 200GPa. We observe a distinct deviation from the ideal metallic behavior between 64 and 110 GPa that suggests pressure-induced H-H interactions. Accompanying ab-initio calculations support this interpretation, as they reveal the formation of an intercalating sublattice of electron density, which enhances the hydrogen contribution to the electronic density of states at the Fermi level. This study shows that pressure induced H-H interactions can occur in metal hydrides at much lower compression and larger H-H distances than previously thought and stimulates an alternative pathway in the search for novel high-temperature superconductors.

cond-mat.mtrl-sci↗

arXiv2018

Observation of Nuclear Quantum Effects and Hydrogen Bond Symmetrisation in High Pressure Ice

Hydrogen bond symmetrisations in H-bonded systems triggered by pressure induced nuclear quantum effects (NQEs) is a long-known concept1 but experimental evidences in high-pressure ices have remained elusive with conventional methods2,3. Theoretical works predicted quantum-mechanical tunneling of protons within water ices to occur at pressures above 30 GPa and the H-bond symmetrisation transition above 60 GPa4. Here, we used 1H-NMR on high-pressure ice up to 90 GPa, and demonstrate that NQEs govern the behavior of the hydrogen bonded protons in ice VII already at significantly lower pressures than previously expected. A pronounced tunneling mode was found to be present up to the highest pressures of 90 GPa, well into the stability field of ice X, where NQEs are not anticipated in a fully symmetrized H-bond network. We found two distinct transitions in the NMR shift data at about 20 GPa and 75 GPa attributed to the step-wise symmetrization of the H-bond (HB), with high-barrier H-Bonds (HBHB) to low-barrier H-bonds (LBHB) and LBHB to symmetric H-bonds (SHB) respectively. These transitions could have major implication on the physical properties of high-pressure ices and planetary interior models. NQEs observed in this chemically simple system over a wide pressure range could prove to be useful in designing a new generation of electronic devices exploiting protonic tunneling.

cond-mat.mtrl-sci↗

arXiv2018

NMR close to Mega-Bar Pressures

The past 15 years have seen an astonishing increase in Nuclear Magnetic Resonance (NMR) sensitivity and accessible pressure range in high-pressure NMR experiments, owing to a series of new developments of NMR spectroscopy applied to the diamond anvil cell (DAC). Recently, with the application of electro-magnetic lenses, so-called Lenz lenses, in toroidal diamond indenter cells, pressures of up to 72 GPa with NMR spin sensitivities of about 10^12 spins/(Hz^1/2) has been achieved. Here, we describe the implementation of a refined NMR resonator structure using a pair of double stage Lenz lenses driven by a Helmholtz coil within a standard DAC, allowing to measure sample volumes as small as 100 pl prior to compression. With this set-up, pressures close to the mega-bar regime (1 Mbar = 100 GPa) could be realised repeatedly, with enhanced spin sensitivities of about 5x10^11 spin/(Hz^1/2). The manufacturing and handling of these new NMR-DACs is relatively easy and straightforward, which will allow for further applications in physics, chemistry, or biochemistry.

physics.app-ph↗

arXiv2018

Journey to the Centre of the Earth: Jule Vernes' dream in the laboratory from an NMR perspective

High pressure nuclear magnetic resonance is among the most challenging fields of research for every NMR spectroscopist due to inherently low signal intensities, inaccessible and ultra-small samples, and overall extremely harsh conditions in the sample cavity of modern high pressure vessels. This review aims to provide a comprehensive overview of the topic of high pressure research and its fairly young and brief relationship with NMR.

physics.app-ph↗

arXiv2017

Magnetic Flux Tailoring through Lenz Lenses in Toroidal Diamond Indenter Cells: A New Pathway to High Pressure Nuclear Magnetic Resonance

A new pathway to nuclear magnetic resonance spectroscopy in high pressure diamond anvil cells is introduced, using inductively coupled broadband passive electro-magnetic lenses to locally amplify the magnetic flux at the isolated sample, leading to an increase in sensitivity. The lenses are adopted for the geometrical restrictions imposed by a toroidal diamond indenter cell, and yield high signal-to-noise ratios at pressures as high as 72 GPa, at initial sample volumes of only 230 pl. The corresponding levels of detection, LODt, are found to be up to four orders of magnitude lower compared to formerly used solenoidal micro-coils in diamond anvil cells, as shown by Proton-NMR measurements on paraffin oil. This approach opens up the field of ultra-high pressure sciences for one of the most versatile spectroscopic methods available in a pressure range unprecedended up to now.

physics.ins-det↗

arXiv2012

Step size of the rotary proton motor in single FoF1-ATP synthase from a thermoalkaliphilic bacterium by DCO-ALEX FRET

Thermophilic enzymes can operate at higher temperatures but show reduced activities at room temperature. They are in general more stable during preparation and, accordingly, are considered to be more rigid in structure. Crystallization is often easier compared to proteins from bacteria growing at ambient temperatures, especially for membrane proteins. The ATP-producing enzyme FoF1-ATP synthase from thermoalkaliphilic Caldalkalibacillus thermarum strain TA2.A1 is driven by a Fo motor consisting of a ring of 13 c-subunits. We applied a single-molecule Förster resonance energy transfer (FRET) approach using duty cycle-optimized alternating laser excitation (DCO-ALEX) to monitor the expected 13-stepped rotary Fo motor at work. New FRET transition histograms were developed to identify the smaller step sizes compared to the 10-stepped Fo motor of the Escherichia coli enzyme. Dwell time analysis revealed the temperature and the LDAO dependence of the Fo motor activity on the single molecule level. Back-and-forth stepping of the Fo motor occurs fast indicating a high flexibility in the membrane part of this thermophilic enzyme.

q-bio.BM↗