Molybdenum disulphide is a layered transition metal dichalcogenide that has recently raised considerable interest due to its unique semiconducting and opto-electronic properties. Although several ...theoretical studies have suggested an electronic phase transition in molybdenum disulphide, there has been a lack of experimental evidence. Here we report comprehensive studies on the pressure-dependent electronic, vibrational, optical and structural properties of multilayered molybdenum disulphide up to 35 GPa. Our experimental results reveal a structural lattice distortion followed by an electronic transition from a semiconducting to metallic state at ~19 GPa, which is confirmed by ab initio calculations. The metallization arises from the overlap of the valance and conduction bands owing to sulphur-sulphur interactions as the interlayer spacing reduces. The electronic transition affords modulation of the opto-electronic gain in molybdenum disulphide. This pressure-tuned behaviour can enable the development of novel devices with multiple phenomena involving the strong coupling of the mechanical, electrical and optical properties of layered nanomaterials.
One of the common features of unconventional superconducting systems such as the heavy-fermion, high transition-temperature cuprate and iron-pnictide superconductors is that the superconductivity ...emerges in the vicinity of long-range antiferromagnetically ordered state. In addition to doping charge carriers, the application of external pressure is an effective and clean approach to induce unconventional superconductivity near a magnetic quantum critical point. Here we report on the discovery of superconductivity on the verge of antiferromagnetic order in CrAs via the application of external pressure. Bulk superconductivity with Tc≈2 K emerges at the critical pressure Pc≈8 kbar, where the first-order antiferromagnetic transition at T(N)≈265 K under ambient pressure is completely suppressed. The close proximity of superconductivity to an antiferromagnetic order suggests an unconventional pairing mechanism for CrAs. The present finding opens a new avenue for searching novel superconductors in the Cr and other transition metal-based systems.
The emergence of a topologically nontrivial vortex-like magnetic structure, the magnetic skyrmion, has launched new concepts for memory devices. Extensive studies have theoretically demonstrated the ...ability to encode information bits by using a chain of skyrmions in one-dimensional nanostripes. Here, we report experimental observation of the skyrmion chain in FeGe nanostripes by using high-resolution Lorentz transmission electron microscopy. Under an applied magnetic field, we observe that the helical ground states with distorted edge spins evolve into individual skyrmions, which assemble in the form of a chain at low field and move collectively into the interior of the nanostripes at elevated fields. Such a skyrmion chain survives even when the width of the nanostripe is much larger than the size of single skyrmion. This discovery demonstrates a way of skyrmion formation through the edge effect, and might, in the long term, shed light on potential applications.
Pressure, as one of the fundamental thermodynamic parameters, can profoundly change the interatomic distances, electronic interactions, chemical bonding and crystal structures, leading to exotic ...structures and properties of materials. High-pressure techniques have significantly impacted disciplines like physics, chemistry, geology, and life science, creating new materials, advancing knowledge of Earth's interior, and influencing pharmaceutical development. This editorial reviews the latest research published in this Collection, highlighting the potential of high-pressure studies to further our understanding of materials’ behavior under extreme conditions.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Searching for superconductivity with T
near room temperature is of great interest both for fundamental science & many potential applications. Here we report the experimental discovery of ...superconductivity with maximum critical temperature (T
) above 210 K in calcium superhydrides, the new alkali earth hydrides experimentally showing superconductivity above 200 K in addition to sulfur hydride & rare-earth hydride system. The materials are synthesized at the synergetic conditions of 160~190 GPa and ~2000 K using diamond anvil cell combined with in-situ laser heating technique. The superconductivity was studied through in-situ high pressure electric conductance measurements in an applied magnetic field for the sample quenched from high temperature while maintained at high pressures. The upper critical field Hc(0) was estimated to be ~268 T while the GL coherent length is ~11 Å. The in-situ synchrotron X-ray diffraction measurements suggest that the synthesized calcium hydrides are primarily composed of CaH
while there may also exist other calcium hydrides with different hydrogen contents.
The search of novel quasi‐1D materials is one of the important aspects in the field of material science. Toroidal moment, the order parameter of ferrotoroidic order, can be generated by a ...head‐to‐tail configuration of magnetic moment. It has been theoretically proposed that 1D dimerized and antiferromagnetic (AFM)‐like spin chain hosts ferrotoroidicity and has the toroidal moment composed of only two antiparallel spins. Here, the authors report a ferrotoroidic candidate of Ba6Cr2S10 with such a theoretical model of spin chain. The structure consists of unique dimerized face‐sharing CrS6 octahedral chains along the c axis. An AFM‐like ordering at ≈10 K breaks both space‐ and time‐reversal symmetries and the magnetic point group of mm′2′allows three ferroic orders in Ba6Cr2S10: (anti)ferromagnetic, ferroelectric, and ferrotoroidic orders. Their investigation reveals that Ba6Cr2S10 is a rare ferrotoroid ic candidate with quasi 1D spin chain, which can be considered as a starting point for the further exploration of the physics and applications of ferrotoroidicity.
Ferrotoroidic order is one of the four primary ferroic order forms. Ba6Cr2S10 is reported to be a rare ferrotoroidic candidate with well‐separated 1D spin chain, where the spins are dimerized and antiferromagnetic‐like coupled and the toroidal moment is composed of only two antiparallel spins.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Tungsten disulfide (WS2) is a layered transition metal dichalcogenide (TMD) that differs from other two-dimensional (2D) compounds such as graphene due to its unique semiconducting, tunable-band-gap ...nature. Multilayered WS2 exhibits an indirect band gap E g of ∼1.3 eV, along with a higher load-bearing ability that is promising for strain-tuning device applications, but the electronic properties of multilayered WS2 at higher strain conditions (i.e., static strain >12%) remain an open question. Here we have studied the structural, electronic, electrical, and vibrational properties of multilayered WS2 at hydrostatic pressures up to ∼35 GPa experimentally in a diamond anvil cell and theoretically using first-principles ab initio calculations. Our results show that WS2 undergoes an isostructural semiconductor-to-metallic (S–M) transition at approximately 22 GPa at 280 K, which arises from the overlap of the highest valence and lowest conduction bands. The S–M transition is caused by increased sulfur–sulfur interactions as the interlayer spacing decreases with applied hydrostatic pressure. The metalization in WS2 can be alternatively interpreted as a 2D to 3D (three-dimensional) phase transition that is associated with a substantial modulation of the charge carrier characteristics including a 6-order decrease in resistivity, a 2-order decrease in mobility, and a 4-order increase in carrier concentration. These distinct pressure-tunable characteristics of the dimensionalized WS2 differentiate it from other TMD compounds such as MoS2 and promise future developments in strain-modulated advanced devices.
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IJS, KILJ, NUK, PNG, UL, UM
Abstract
The iron-based superconductor is emerging as a promising platform for Majorana zero mode, which can be used to implement topological quantum computation. One of the most significant advances ...of this platform is the appearance of large vortex level spacing that strongly protects Majorana zero mode from other low-lying quasiparticles. Despite the advantages in the context of physics research, the inhomogeneity of various aspects hampers the practical construction of topological qubits in the compounds studied so far. Here we show that the stoichiometric superconductor LiFeAs is a good candidate to overcome this obstacle. By using scanning tunneling microscopy, we discover that the Majorana zero modes, which are absent on the natural clean surface, can appear in vortices influenced by native impurities. Our detailed analysis reveals a new mechanism for the emergence of those Majorana zero modes, i.e. native tuning of bulk Dirac fermions. The discovery of Majorana zero modes in this homogeneous material, with a promise of tunability, offers an ideal material platform for manipulating and braiding Majorana zero modes, pushing one step forward towards topological quantum computation.
Activated carbon was treated at 5
GPa up to 1600
°C, and the structural evolution in the graphitization process was investigated. The graphitization temperature is equal to 1200
°C at 5
GPa, ...reflected by X-ray diffraction (XRD) patterns. Honeycomb-like structures in micron scale come into being in the high-pressure sintering temperature range of 1000−1100
°C and slice-like structures appear after graphitization. The existence of D and D’ lines in the Raman spectra for the graphitized-activated carbon indicates that there are still some disordered structures. The continuous occurrence of variable-range hopping, the approximately linear
ρ–T relationship, and semimetal conduction mechanism accords with the graphitization process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The superconducting state properties of the CuBa2Ca3Cu4O10+δ (Cu-1234) system, with a transition temperature as high as 117.5 K, were investigated. The ac magnetic susceptibility measurements ...confirmed a very sharp transition to the superconducting state. The upper critical field, Hc2, as high as 91 T, and the irreversibility field, Hirr, as high as 21 T at 77 K, were determined using dc SQUID magnetization measurements. The intragrain critical current density, jc, estimated from a magnetic hysteresis loop, is as high as 5 × 109 A/m2 in a self-generated magnetic field at 77 K. However, the intergrain critical current density in the studied material is smaller by four orders of magnitude due to very weak intergrain connections.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK