GaAs P-HEMT MMICs for K-to-Ka band wireless communications

Ishikawa, T.; Ishida, Takao; Komaru, M.; Chaki, S.; Fujimoto, Shigeyuki; Katoh, Takayuki

doi:10.1109/etwcs.1999.897324

Cited by 7 publications

(5 citation statements)

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“…or 2, about a quarter of century ago in the context of superfluid 3 He [24]. Very recently, the reality of this intrinsic magnetic moment has caused a renewed interest in the magnetic property of the chiral superconducting state of Sr 2 RuO 4 [25]. At low enough temperature T ≪ T c , the intrinsic magnetic moment is M in ≃ (N/2)µ B (m/m band ) ℓ.…”

Section: Two Phases In T-h Phase Diagrammentioning

confidence: 99%

“…where N in is the order of the superfluid electron density N s [22][23][24], while lively disputes were carried out concerning the size of N in , whether N in ∼ O(N s ) or O(N s (T c / * F ) n ) with n = 1 or 2, about a quarter of century ago in the context of superfluid 3 He [25]. Very recently, the reality of this intrinsic magnetic moment has caused a renewed interest in the magnetic property of the chiral superconducting state of Sr 2 RuO 4 [26]. At low enough temperature T T c , the intrinsic magnetic moment is M in (N/2)µ B (m/m band ) .…”

Section: Two Phases In T -H Phase Diagrammentioning

confidence: 99%

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Theory of a new type of heavy-electron superconductivity in PrOs₄Sb₁₂: quadrupolar-fluctuation mediated odd-parity pairings

Miyake

Kohno

Harima

2003

J. Phys.: Condens. Matter

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It is shown that unconventional nature of superconducting state of PrOs 4 Sb 12 , a Pr-based heavy electron compound with the filled-Skutterudite structure, can be explained in a unified way by taking into account the structure of the crystallineelectric-field (CEF) level, the shape of the Fermi surface determined by the band structure calculation, and a picture of the quasiparticles in f 2 -configuration with magnetically singlet CEF ground state. Possible types of pairing are narrowed down by consulting recent experimental results. In particular, the chiral "p"-wave states such as p x + ip y is favoured under the magnetic field due to the orbital Zeeman effect, while the "p"-wave states with two-fold symmetery such as p x can be stabilized by a feedback effect without the magnetic field. It is also discussed that the double superconducting transition without the magnetic field is possible due to the spin-orbit coupling of the "triplet" Cooper pairs in the chiral state.Recently, the superconductivity has been found in heavy electron compound PrOs 4 Sb 12 with the crystal structure of the filled Skutterudite [1]. Since the specific heat jump ∆C at the superconducting transition temperature T c =1.8K is quite enhanced as ∆C/T c ≃ 500 mJ/K 2 mole, heavy quasiparticles are responsible for the Cooper pair formation. Quite recently, a measurement of the longitudinal relaxation rate, 1/T 1 , of NQR at Sb site has been performed and very unusual temperature (T ) dependence was revealed both for T < T c and T > T c [2], while the normal state properties had been known to be also quite unconventional [1,3]. Unconventional behaviors of 1/T 1 are summarized as follows: 1) Pseudo gap behavior is seen in 1/T 1 T at T c < T < 2T c , in which the resistivity ρ also shows a pseudo-gap behavior [1]. 2) There is no trace of the coherence (Hebel-Slichter) peak around T = T c at all. 3) 1/T 1 appears to exhibit an exponential T -dependence below 1.3T c , giving the superconducting gap ∆ in the low temperature limit as 2∆/k B T c ≃ 5.3, although a possibility is not ruled out that the crossover to the T 3 -dependence begins to be observed at around T ≃ T c /3 the lowest temperature covered by experiments.Very recently, the anomaly of specific heat near T c has been observed, which suggests a double transition at T = T c1 and T c2 (T c2 < T c1 ) [3,4] It also turned out very recently on the basis of measurements of the angular dependence of the thermal conductivity κ under the magnetic field H [5] that there exsist at least two different superconducting phases in the T -H phase diagram. In the low-field phase, the 2-fold component of κ z along the z-direction is observed as a function of the angle of the direction of H around the z-axis, while the 4-fold one is observed in the high-field phase. The phase boundary approaches the lower critical temperature T c2 as H → 0. This is in marked contrast with the case of a heavy electron superconductor CeCoIn 5 where the data can be interpreted by a simple "d"-wave model [6]. These behaviors s...

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Section: Two Phases In T-h Phase Diagrammentioning

confidence: 99%

Section: Two Phases In T -H Phase Diagrammentioning

confidence: 99%

Theory of a new type of heavy-electron superconductivity in PrOs₄Sb₁₂: quadrupolar-fluctuation mediated odd-parity pairings

Miyake

Kohno

Harima

2003

J. Phys.: Condens. Matter

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“…C(T ) ∝ T 2 and T −1 1 ∝ T 3 at low temperatures. 12,13) These temperature dependences are interpreted as a consequence of the line nodes of the energy gap. The residual density of states observed in the previous experiments may be due to the impurity effects on the anisotropic superconductivity with line nodes.…”

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confidence: 99%

Spin-Triplet Superconductivity with Line Nodes in Sr₂RuO₄

2000

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Several possible odd-parity states are listed up group-theoretically and examined in light of recent experiments on Sr2RuO4. Those include some of the f -wave pairing states, d(k) ∝ zkxky(kx + iky) andẑ(k 2 x − k 2 y )(kx + iky) and otherẑ(kx + iky) cos ckz (c is the c-axis lattice constant) as most plausible candidates. These are time-reversal symmetry broken states and have line nodes running either vertically (the former two) or horizontally (the latter), consistent with experiments. Characterizations of these states and other possibilities are given.KEYWORDS: spin triplet superconductivity, line node of the energy gap, time-reversal symmetry breakingThe possibility of the spin triplet pairing in Sr 2 RuO 4 is pointed out 1) soon after the discovery of the superconductivity.2) Experimental evidence for the spin triplet pairing is accumulated. The temperature-independent Knight shift for the external magnetic field parallel to the conducting plane (the basal plane) is thought to be the evidence for the spin triplet pairing with the d-vector aligned to the z-axis.3) The µSR experiment 4) indicates that the magnetic field is spontaneously induced and the time reversal symmetry seems to be broken in the superconducting state. These experiments were explained by the p-wave spin triplet state with the order parameter,where ∆ 0 is a constant. This state is analogous to the Anderson-Brinkman-Morel (ABM) state, which is identified as the A phase in superfluid 3 He.7) The AMB state in superfluid 3 He has point nodes of the energy gap at k x = k y = 0 on the spherical Fermi surface. However, since the Fermi surface of Sr 2 RuO 4 consists of three cylindrical surfaces, the above p-wave state has a finite energy gap on the Fermi surface. The previous experiments of specific heat 8) C(T ) and NMR relaxation rateshowed that about a half of the density of states remains at T = 0 in the superconducting state. In order to explain this residual density of states, the non-unitary states and the orbital dependent superconductivity are proposed. 10, 11)However, it is reported in very recent experiments that the residual density of states are very small in the better samples, i.e. C(T ) ∝ T 2 and T −1 1∝ T 3 at low temperatures.12, 13) These temperature dependences are interpreted as a consequence of the line nodes of the energy gap. The residual density of states observed in the previous experiments may be due to the impurity effects on the anisotropic superconductivity with line nodes.An anisotropic energy gap model caused by the finite range interaction in the two-dimensional plane is proposed to explain the line-node-like temperature dependences of the specific heat and relaxation rate in Sr 2 RuO 4 .14) The order parameter in this case is given bywhere a is the lattice constant in the basal plane of the tetragonal crystal D 4h . This anisotropic energy gap should give the exponential temperature dependence as exp(−α∆/T ) at temperatures below the smallest energy gap ∆ in clean samples, where α is a constant of the order 1. As ...

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“…sign of the linear term of N (ξ), the extra magnetization change arises under the external magnetic field H. This mechanism was first predicted almost four decades ago by S. Takagi as a possible effect of discontinuity in the spin susceptibility of superfluid 3 He at the critical temperature T c where 3 He exhibits a second-order phase transition from the normal to the A phase at H = 0. 5 The paper by Takagi also predicted that in the A1 phase there exists an extra spin-polarization independent of H other than the BCS-type contribution.…”

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confidence: 94%

“…4 In this sense, it is desired to give a theoretical explanation for this phenomenon reported by Ishida. 3 In this Letter we discuss theoretically the mechanism for such an extra magnetization in Sr 2 RuO 4 , which is considered to be in the spin-triplet ESP superconducting state, under the external magnetic field. This gives an explanation for the recent observation of extra magnetization in Sr 2 RuO 4 .…”

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confidence: 99%

Theory of Pairing Assisted Spin Polarization in Spin-Triplet Equal Spin Pairing: Origin of Extra Magnetization in Sr₂RuO₄ in Superconducting State

Miyake

2014

J. Phys. Soc. Jpn.

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It is shown that an extra magnetization is induced by an onset of the equal-spin-pairing of spin triplet superconductivity if the energy dependence of the density of states of quasiparticles exists in the normal state. It turns out that the effect is observable in Sr 2 RuO 4 due to the existence of van Hove singularity in the density of states near the Fermi level, explaining the extra contribution in the Knight shift reported by Ishida et al . It is also quite non-trivial that this effect exists even without external magnetic field, which implies that the time reversal symmetry is spontaneously broken in the spin space. Properties of the Fermi superfluidity sustained by the triplet pairing have been discussed extensively since the discovery of superfluid 3 He in 1972, and its fundamental aspects seem to have been clarified so far. 1 On the other hand, it has recently been measured by the Knight shift that the magnetization of Sr 2 RuO 4 , which is considered to be a triplet superconductor in the equal-spin-pairing (ESP) state, 2 exhibits an extra magnetization under the external magnetic field other than that expected in the ESP state. 3 This phenomenon cannot be understood in the framework of spin-singlet pairing state, while some researchers doubt the spin-triplet state because the first-order superconducting transition has been observed under the magnetic field which is characteristic of the paramagnetic effect in the spin-singlet pairing state. 4 In this sense, it is desired to give a theoretical explanation for this phenomenon reported by Ishida. 3 In this Letter we discuss theoretically the mechanism for such an extra magnetization in Sr 2 RuO 4 , which is considered to be in the spin-triplet ESP superconducting state, under the external magnetic field. This gives an explanation for the recent observation of extra magnetization in Sr 2 RuO 4 . 3 A physical reason for this extra contribution is rather simple. Under the magnetic field, the density of states (DOS) of the normal state quasiparticles of up-spin, N ↑ (ξ), and those of down-spin, N ↓ (ξ), are different if the particle-hole symmetry is apparently broken, i.e., N (ξ)'s are not constant but have a considerable linear term in the quasiparticle energy ξ measured from the chemical potential. Then, the free energy gains associated with Cooper pair condensation are different in general, resulting in a redistribution of up-spin and downspin components so as to gain much more condensation energy. Therefore, depending on the

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GaAs P-HEMT MMICs for K-to-Ka band wireless communications

Cited by 7 publications

References 1 publication

Theory of a new type of heavy-electron superconductivity in PrOs₄Sb₁₂: quadrupolar-fluctuation mediated odd-parity pairings

Theory of a new type of heavy-electron superconductivity in PrOs₄Sb₁₂: quadrupolar-fluctuation mediated odd-parity pairings

Spin-Triplet Superconductivity with Line Nodes in Sr₂RuO₄

Theory of Pairing Assisted Spin Polarization in Spin-Triplet Equal Spin Pairing: Origin of Extra Magnetization in Sr₂RuO₄ in Superconducting State

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GaAs P-HEMT MMICs for K-to-Ka band wireless communications

Cited by 7 publications

References 1 publication

Theory of a new type of heavy-electron superconductivity in PrOs4Sb12: quadrupolar-fluctuation mediated odd-parity pairings

Theory of a new type of heavy-electron superconductivity in PrOs4Sb12: quadrupolar-fluctuation mediated odd-parity pairings

Spin-Triplet Superconductivity with Line Nodes in Sr2RuO4

Theory of Pairing Assisted Spin Polarization in Spin-Triplet Equal Spin Pairing: Origin of Extra Magnetization in Sr2RuO4 in Superconducting State

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Theory of a new type of heavy-electron superconductivity in PrOs₄Sb₁₂: quadrupolar-fluctuation mediated odd-parity pairings

Theory of a new type of heavy-electron superconductivity in PrOs₄Sb₁₂: quadrupolar-fluctuation mediated odd-parity pairings

Spin-Triplet Superconductivity with Line Nodes in Sr₂RuO₄

Theory of Pairing Assisted Spin Polarization in Spin-Triplet Equal Spin Pairing: Origin of Extra Magnetization in Sr₂RuO₄ in Superconducting State