Quantum Critical Point of Itinerant Antiferromagnet in the Heavy Fermion Ce(Ru_{1-x}Rh_x)_2Si_2

A focus of recent experimental and theoretical studies on heavy fermion systems close to antiferromagnetic (AFM) quantum critical points (QCP) is directed toward revealing the nature of the fixed point, i.e., whether it is an itinerant antiferromagnet [spin density wave (SDW)] type or a locally-critical fixed point. The relevance of the local QCP was proposed to explain the E/T-scaling with an anomalous exponent observed for the AFM QCP of CeCu_{5.9}Au_{0.1}. In this work, we have investigated an AFM QCP of another archetypal heavy fermion system Ce(Ru_{1-x}Rh_x)_2Si_2 with x = 0 and 0.03 (sim x_c) using single-crystalline neutron scattering. Accurate measurements of the dynamical susceptibility Im[chi(Q,E)] at the AFM wave vector Q = 0.35 c^* have shown that Im[chi(Q,E)] is well described by a Lorentzian and its energy width Gamma(Q), i.e., the inverse correlation time depends on temperature as Gamma(Q) = c_1 + c_2 T^{3/2 +- 0.1}, where c_1 and c_2 are x dependent constants, in low temperature ranges.This critical exponent 3/2 proves that the QCP is controlled by the SDW QCP in three space dimensions studied by the renormalization group and self-consistent renormalization theories.Comment: 4 pages, 4 figures, LT24 (Aug. 2005, Orlando

Thermomechanical noise of arrayed capacitive accelerometers with 300-NM-gap sensing electrodes

2017 19th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS), 18-22 June 2017.Thermomechanical noise of arrayed capacitive accelerometers with sub-micrometer sensing electrodes was evaluated. The unit accelerometer of the array was 80-μm square, designed as a proportional scale-down of a conventional single-axis accelerometer. Since the size effect shows the capacitance sensitivity per unit volume increases by proportional downsizing, a 10-by-10 array of the one-tenth sized unit accelerometer would have the same sensitivity of a single accelerometer of same occupied area. However, the thermomechanical noise needs to be controlled and reduced by vacuum encapsulation because size reduction causes noise increase. By measuring the electrical impedance at the resonant frequency, the damping coefficient was estimated using electrical equivalent circuit modeling. The estimated thermomechanical noise was reduced below 3 μg√VHZ by encapsulating at 100 Pa, which is low enough for instrumentation applications

Zernike generation with MEMS deformadle mirror actuated by electrostatic piston array

2018 IEEE Micro Electro Mechanical Systems (MEMS), 21-25 Jan. 2018.We report a low-voltage and large-displacement electrostatic deformable mirror for in vivo retinal imaging by adaptive-optics optical coherence tomography. The mirror utilizes an electrostatic piston actuator which allows bottom electrodes to move vertically to keep the gap small to maintain large actuation force at low actuation voltage. An 8-mm-diameter mirror device was fabricated from two components; the mirror part and the actuator part. The parts were assembled with 7-μm-gap defined by an SU-8 layer. We successfully demonstrated operation of the mirror in various Zernike modes

Novel slow dynamics of phase transition in the partially ordered frustrated magnet DyRu2Si2

DyRu2Si2 is a frustrated magnet to exhibit multiple magnetic phase transition in zero and finite magnetic fields. We investigated and characterized the phase transition between the partially-ordered antiferromagnetic phases at zero field by ac susceptibility measurements. Detailed ac susceptibility measurements reveal the novel critical dynamics of the phase transition; extremely slow dynamics with the relaxation time in the order of 10-100 msec, speed-up of the dynamics on cooling indicating its non-thermally activated origin and growing of the ferromagnetic correlations towards the phase transition temperature. On the basis of these findings, we propose the novel phase transition process, namely, the spontaneous striped-arrangement of the precedently emergent "belt-like" ferromagnetic spin texture.Comment: Accepted by JPSJ URL:https://journals.jps.jp/doi/10.7566/JPSJ.92.09470

Quantum Critical Point of Itinerant Antiferromagnet in Heavy Fermion

A quantum critical point (QCP) of the heavy fermion Ce(Ru_{1-x}Rh_x)_2Si_2 (x = 0, 0.03) has been studied by single-crystalline neutron scattering. By accurately measuring the dynamical susceptibility at the antiferromagnetic wave vector k_3 = 0.35 c^*, we have shown that the energy width Gamma(k_3), i.e., inverse correlation time, depends on temperature as Gamma(k_3) = c_1 + c_2 T^{3/2 +- 0.1}, where c_1 and c_2 are x dependent constants, in a low temperature range. This critical exponent 3/2 +- 0.1 proves that the QCP is controlled by that of the itinerant antiferromagnet.Comment: 4 pages, 3 figure