scholarly journals Evidence for a pressure-induced antiferromagnetic quantum critical point in intermediate-valence UTe2

2020 ◽  
Vol 6 (42) ◽  
pp. eabc8709 ◽  
Author(s):  
S. M. Thomas ◽  
F. B. Santos ◽  
M. H. Christensen ◽  
T. Asaba ◽  
F. Ronning ◽  
...  
Keyword(s):  
Ambient Pressure ◽  
Applied Pressure ◽  
Quantum Critical Point ◽  
Antiferromagnetic Order ◽  
Intermediate Valence ◽  
Ac Calorimetry ◽  
Unconventional Superconductor ◽  
Spin Triplet ◽  
Magnetic States ◽  
Low Pressures

UTe2 is a recently discovered unconventional superconductor that has attracted much interest because of its potentially spin-triplet topological superconductivity. Our ac calorimetry, electrical resistivity, and x-ray absorption study of UTe2 under applied pressure reveals key insights on the superconducting and magnetic states surrounding pressure-induced quantum criticality at Pc1 = 1.3 GPa. First, our specific heat data at low pressures, combined with a phenomenological model, show that pressure alters the balance between two closely competing superconducting orders. Second, near 1.5 GPa, we detect two bulk transitions that trigger changes in the resistivity, which are consistent with antiferromagnetic order, rather than ferromagnetism. Third, the emergence of magnetism is accompanied by an increase in valence toward a U4+ (5f2) state, which indicates that UTe2 exhibits intermediate valence at ambient pressure. Our results suggest that antiferromagnetic fluctuations may play a more substantial role on the superconducting state of UTe2 than previously thought.

DC Magnetic Susceptibility of CeCoGe2.36Si0.64 under High Pressure

2012 ◽  
Vol 190 ◽  
pp. 405-408
Author(s):  
J.J. Larrea ◽  
J. Teyssier ◽  
H. Ronnow ◽  
M. Müller ◽  
A. Sidorenko ◽  
...  
Keyword(s):  
High Pressure ◽  
Magnetic Susceptibility ◽  
Heavy Fermion ◽  
Pressure Range ◽  
Magnetic Phase ◽  
Ambient Pressure ◽  
Quantum Critical Point ◽  
Magnetic Phase Diagram ◽  
Antiferromagnetic Order

We report an investigation of the magnetic phase diagram of the heavy fermion com-pound CeCoGe2.36Si0.64 using DC magnetic susceptibility measurements under high pressure upto 10 kbar. The antiferromagnetic order that develops at ambient pressure below about 5.5 Kremains essentially unaffected by pressure in the investigated pressure range up to 10 kbar. Onthe other hand, moderate magnetic fields appear to induce a quantum critical point in a sam-ple subject to a pressure of 2 kbar. We discuss the role of disorder in the series of compoundsCeCoGe3−xSix.

Micro-Feature Replication via Polymer Molding at Ambient Pressure

2007 ◽  
Author(s):  
Varun Thakur ◽  
Peiman Mosaddegh ◽  
David C. Angstadt
Keyword(s):  
Amorphous Materials ◽  
Ambient Pressure ◽  
Applied Pressure ◽  
Crystalline Polymer ◽  
Lower Surface ◽  
Mold Temperature ◽  
Silicon Mold ◽  
Aspect Ratios ◽  
Molded Parts ◽  
Micro Features

The study focuses on the ability of a polymer to replicate micro-features when processed at an elevated mold temperature without externally applied pressure. Replication is performed using four different polymers—High Density Polyethylene (HDPE), Polypropylene (PP), Polystyrene (PS), and Poly (Methyl Methacrylate) (PMMA) on a silicon mold containing surface features as small as 500nm. Feature replication is assessed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) to compare feature dimensions of the mold to those of the replicated parts. Shrinkage in dimensions is observed to be anisotropic in the molded parts and its extent of varies among the different polymers. Crystalline HDPE shows a higher degree of shrinkage relative to amorphous polymers such as PS and PMMA. These results verify the theoretical value of shrinkage calculated from the coefficient of volumetric shrinkage values and density. By increasing the mold temperature well above the melting point of the polymer, a depth ratio of 70–80% can be achieved in parts having aspect ratios of around 0.5. The result is comparable to the values achieved by similar studies. Varying aspect ratios are fully replicated by all four polymers at elevated mold temperature. This clearly shows that increasing mold temperature results in significant improvement in depth ratios for micro-featured parts. The amorphous materials provide better feature replication and lower surface roughness than the semi-crystalline polymer.

scholarly journals Observation of half-quantum flux in the unconventional superconductor β-Bi2Pd

Science ◽  
2019 ◽  
Vol 366 (6462) ◽  
pp. 238-241 ◽  
Author(s):  
Yufan Li ◽  
Xiaoying Xu ◽  
M.-H. Lee ◽  
M.-W. Chu ◽  
C. L. Chien
Keyword(s):  
Magnetic Flux ◽  
Pairing Symmetry ◽  
Quantum Oscillation ◽  
Unconventional Superconductivity ◽  
Unconventional Superconductor ◽  
Quantum Bits ◽  
Flux Quantization ◽  
Triplet Pairing ◽  
Quantum Flux ◽  
Spin Triplet

Magnetic flux quantization is one of the defining properties of a superconductor. We report the observation of half-integer magnetic flux quantization in mesoscopic rings of superconducting β-Bi2Pd thin films. The half-quantum fluxoid manifests itself as a π phase shift in the quantum oscillation of the superconducting critical temperature. This result verifies unconventional superconductivity of β-Bi2Pd and is consistent with a spin-triplet pairing symmetry. Our findings may have implications for flux quantum bits in the context of quantum computing.

scholarly journals Ambient Pressure Structural Quantum Critical Point in the Phase Diagram of(CaxSr1−x)3Rh4Sn13

2015 ◽  
Vol 114 (9) ◽  
Author(s):  
S. K. Goh ◽  
D. A. Tompsett ◽  
P. J. Saines ◽  
H. C. Chang ◽  
T. Matsumoto ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Critical Point ◽  
Ambient Pressure ◽  
Quantum Critical Point ◽  
Quantum Critical

scholarly journals ON DISCOVERY OF THE FERROMAGNETIC SUPERCONDUCTOR UCoGe

2011 ◽  
Vol 14 (2) ◽  
pp. 21-28
Author(s):  
Huy Thanh Nguyen ◽  
Cuong Duc Dao ◽  
Thu Thanh Vu ◽  
An Tu Bui
Keyword(s):  
Transition Temperature ◽  
Curie Temperature ◽  
Ambient Pressure ◽  
Spin Fluctuations ◽  
Resistive Transition ◽  
Unconventional Superconductor ◽  
Present Evidence ◽  
Microscopic Scale ◽  
Weak Ferromagnet ◽  
Curie Temperature Tc

We report the coexistence of ferromagnetic order and superconductivity in UCoGe at ambient pressure. The data obtained from the basic thermal, magnetic and transport properties on the macro and microscopic scale show that UCoGe is a weak ferromagnet with a Curie temperature TC = 3 K, and also, is a superconductor with a resistive transition temperature Ts = 0.8 K. Those present evidence that UCoGe is an unconventional superconductor and argue that superconductivity is mediated by critical ferromagnetic spin fluctuations.

scholarly journals New electronic perovskite oxides from beyond high pressure synthesis

2014 ◽  
Vol 70 (a1) ◽  
pp. C615-C615
Author(s):  
J Attfield
Keyword(s):  
High Pressure ◽  
Ambient Pressure ◽  
Structural Phase ◽  
Quantum Critical Point ◽  
Negative Thermal Expansion ◽  
Charge Order ◽  
Stability Field ◽  
Soft Chemistry ◽  
Volume Collapse ◽  
Post Synthesis

Materials synthesised from high pressure (HP) conditions offer a variety of possibilities for the discovery of new electronic and magnetic phenomena. Recovery of a solid to ambient pressure (AP) from its HP thermodynamic stability field effectively introduces a large negative pressure that can drive the material into an unusual electronic ground state; as illustrated by HP structural and property studies of PbRuO3 and BiNiO3. PbRuO3 is synthesised at 10 GPa and shows an orbitally ordered phase at AP and low temperatures that is suppressed at an apparent quantum critical point near 6 GPa [1]. A new structural phase emerges at much higher pressures ~30 GPa. BiNiO3 synthesised at 6 GPa shows an unusual charge order that is suppressed at 3.4 GPa; the transition is associated with a volume collapse leading to colossal negative thermal expansion [2]. Materials recovered from HP are also precursors for 'hard-soft' chemistry, where the instability of a dense precursor from `hard' HP conditions is relieved through `soft' post-synthesis modification. We recently demonstrated this concept for the HP phase SrCrO3 which on reduction gives two new phases SrCrO2.80 and SrCrO2.75 with long period oxygen vacancy, charge and spin ordered superstructures [3]. These studies have been carried out in collaboration with co-authors of the papers below.

Evolution of Superconducting and Hidden Order Phases in URu2Si2 Under Applied Pressure

2008 ◽  
Vol 1104 ◽  
Author(s):  
M. Brian Maple ◽  
Jason R. Jeffries ◽  
Nicholas P. Butch ◽  
Benjamin T. Yukich
Keyword(s):  
Critical Field ◽  
Pressure Dependence ◽  
Ambient Pressure ◽  
Applied Pressure ◽  
Upper Critical Field ◽  
Qualitative Change ◽  
Resistivity Measurements ◽  
Surface Fraction ◽  
Hidden Order ◽  
Two Phases

AbstractElectrical resistivity measurements performed under applied hydrostatic pressure and in magnetic fields have been used to probe the hidden order (HO) and superconducting (SC) states of URu2Si2, which have ambient-pressure transition temperatures TO = 17.5 K and Tc = 1.5 K, respectively. TO increases with applied pressure and a distinct kink in its pressure dependence is observed at 15 kbar; this feature is associated with the onset of antiferromagnetism. The pressure dependence of the SC upper critical field has been measured with the external field aligned parallel to both crystalline axes. The SC phase is smoothly suppressed to a critical pressure of about 15 kbar and no qualitative change in the critical field curves is observed. The co-evolution of the HO and SC phases is discussed within the context of a model in which the two phases compete for Fermi surface fraction.

scholarly journals Pressure-tuned quantum criticality in the antiferromagnetic Kondo semimetal CeNi2−δAs2

2015 ◽  
Vol 112 (44) ◽  
pp. 13520-13524 ◽  
Author(s):  
Yongkang Luo ◽  
F. Ronning ◽  
N. Wakeham ◽  
Xin Lu ◽  
Tuson Park ◽  
...  
Keyword(s):  
Electrical Transport ◽  
Carrier Density ◽  
Quantum Critical Point ◽  
Quantum Criticality ◽  
Kondo Lattice ◽  
Antiferromagnetic Order ◽  
Zero Temperature ◽  
Electrical Transport Properties ◽  
Continuous Transition ◽  
Quantum Critical

The easily tuned balance among competing interactions in Kondo-lattice metals allows access to a zero-temperature, continuous transition between magnetically ordered and disordered phases, a quantum-critical point (QCP). Indeed, these highly correlated electron materials are prototypes for discovering and exploring quantum-critical states. Theoretical models proposed to account for the strange thermodynamic and electrical transport properties that emerge around the QCP of a Kondo lattice assume the presence of an indefinitely large number of itinerant charge carriers. Here, we report a systematic transport and thermodynamic investigation of the Kondo-lattice system CeNi2−δAs2 (δ ≈ 0.28) as its antiferromagnetic order is tuned by pressure and magnetic field to zero-temperature boundaries. These experiments show that the very small but finite carrier density of ∼0.032 e−/formular unit in CeNi2−δAs2 leads to unexpected transport signatures of quantum criticality and the delayed development of a fully coherent Kondo-lattice state with decreasing temperature. The small carrier density and associated semimetallicity of this Kondo-lattice material favor an unconventional, local-moment type of quantum criticality and raises the specter of the Nozières exhaustion idea that an insufficient number of conduction-electron spins to separately screen local moments requires collective Kondo screening.

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