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- PostProbing electronic nematicity and anisotropic electron-phonon coupling in strained YBCO nanowires(2024) Rongrueangkul, Karn; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Lombardi, Floriana; Kalaboukhov, Alexei; Bauch, ThiloDespite nearly 40 years since its discovery in 1986, the underlying mechanism behind the high-temperature superconductivity (HTS) in cuprates remains a significant enigma in condensed matter physics. The existence of multiple intertwined local orders, originating from the strongly correlated electrons, further complicates the study of these materials. Such complexity of the normal state is depicted in a very intricate temperature-doping phase diagram. A way to advance the knowledge of these materials is to tune the local orders, both in the superconducting and in the normal state, to disentangle them for individual study. One way to achieve such an effect is to apply strain to the cuprates in nm-thick films. Previously, it was discovered that the unidirectional strain, induced by few-unit-cell-thick films deposited on a nanostructured surface, can modify the charge order and cause the in-plane resistivity of the films to become much more anisotropic than in bulk materials. According to the Boltzmann transport model, such anisotropy in the in-plane resistivity is due to the directional modification of the Fermi velocity in which the velocity along one crystallographic in-plane direction is much higher than another. This results in an anisotropic Fermi surface that connects to the presence of an electronic nematicity, wherein the electronic structure retains translational symmetry while spontaneously breaking rotational symmetry. In earlier reports on the archetypal HTS YBa2Cu3O7−δ (YBCO) superconductor, the photoemission and transport measurements appear to show that electron-phonon coupling (EPC) can become directionally suppressed if the Fermi surface becomes nematic (as in our sample). This should strongly affect the heat transport in nm-thick YBCO films. Hence, the focus of this thesis work is to investigate the anisotropic EPC through the study of electrical and heat transport properties of YBCO nanowires oriented along different crystallographic axes. The nanowires are fabricated from YBCO thin films epitaxially grown by the Pulsed Laser Deposition technique, and the strain is tuned by modifying the film thickness.
- PostCharacterisation of Recycled Plastics for Automotive Radar Applications at 77 GHz(2023) Nourjoo, Mohammad; Ameerudeen, Mohamed Azad; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Stake, Jan; Bevilacqua, StellaThis work investigates the potential of various recycled plastic materials for use in bumper areas which are in closer proximity to automotive radar systems operating at 77 GHz. The study focuses on both experimental and analytical calculation approaches to assess the electromagnetic properties of these materials, specifically focusing on their complex permittivity and loss tangent characteristics at 77 GHz. For this purpose, a quasi-optical measurement setup which utilises metallic reflective mirrors to narrow and collimate the beam of waves produced by WR12 frequency extenders in the 65-90 GHz range is used. The S-parameters measured by the Vector Network Analyzer (VNA) of the samples are utilised to calculate the complex refractive index. This procedure allows for the determination of the permittivity and loss tangent for each specific sample material. To ensure the robustness of the calculation method, the known permittivity and loss tangent values at 77 GHz from a reference non-recycled material provided by the supplier are utilised to calculate theoretical S-parameters, which are then employed in the same method to re-evaluate the permittivity and loss tangent. This process enables a direct comparison with the initial VNA-derived results. This round-trip verification process confirms the reliability of the calculation method used in the analysis. From the analysis of all test materials, a particular recycled plastic material is chosen, suggesting its potential suitability for use in automotive bumper production. Overall, this research offers significant insights into the development of radar-compatible recycled plastics for bumper design and manufacturing.
- PostPitch Measurements on Chirally Doped Ferroelectric Nematics(2023) Jonsson, Patrick; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Rudquist, Per; Rudquist , PerFollowing the recent discovery of the ferronematic liquid crystal phase, it is important to explore the material’s properties as well as to devise methods of identification. In this report, an experimental method to measure the helical pitch of the ferronematic material RM734 doped with a chiral dopant S811 by use of the so-called circularly rubbed cell method is explored for the first time and compared to other methods. The method utilises a cell of two substrates linearly and circularly rubbed of which the pitch is measured from the resulting deviation angle of disclination lines induced by this particular geometry. The results showed that the pitch in the polar ferroelectric phase behaved similarly to that of the non-polar nematic phase but with a small change in magnitude at the phase transition to the polar phase. Phase transition temperatures could also be determined and a negative trend between the doping concentrations and transition temperatures for both the isotropic to nematic and nematic to ferronematic phases was observed. Finally, a first attempt was made at in-situ ultraviolet light-induced polymer stabilisation of the ferronematic liquid crystal by use of photoreactive monomers mixed into the liquid crystal. This attempt yielded inconclusive results as polymer stabilisation was not observed, yet there seemed to be some adverse effects on the liquid crystal.
- PostDesign and Validation of a Concurrent Dual-Band GaN Doherty Power Amplifier(2023) Ur Rasool Haider, Jamal; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Fager, Christian; Saad, Paul; Hou, Rui; Zhou, HanIn the current era characterized by rapid advancements in wireless communication, the demand for high data rates, multi-band operation and low power consumption in communication systems like mobile base stations, poses significant challenges. To address these challenges, it is imperative to explore and devise new power amplifier (PA) solutions that conform to these stringent requirements. This thesis presents a comprehensive solution in the form of a dual-band Doherty PA (DB-DPA) to meet these pressing requirements. DPAs have gained considerable popularity due to their ability to achieve high back-off efficiency across a wide range of output power levels. The primary objective of this research is to design and simulate a symmetrical DB-DPA using state-of-the-art GaN-HEMT technology, for the frequency bands of 1.85 and 2.65 GHz. The load modulation network comprises a wideband combiner followed by a Chebyshev transformer. Subsequently, the designed DB-DPA is fabricated, measured, and the obtained results are presented and analyzed in detail. Through extensive measurements, this study demonstrates that the proposed DBDPA design delivers satisfactory performance in terms of drain efficiency (DE) and power gain for both the lower and upper-frequency bands of 1.85/2.65 GHz with a bandwidth of 100 MHz each. At a peak power of 47.9/47.3 dBm, the DB-DPA achieves a DE of 55.6/54.5%. Furthermore, at a 6 dB back-off level, the DB-DPA exhibits a DE of 41.2/44.6% and a gain of 19.5/15 dB for the desired frequencies. These characteristics position this design as a promising candidate for communication applications. The findings presented in this research emphasize the potential of the proposed DB-DPA design and provide a viable solution that meets the growing requirements of the wireless industry. The comprehensive investigation conducted through simulations and measurements contributes to the body of knowledge in the field and provides valuable insights for further advancements in DB-DPA design.
- PostAnyon Colliders: A time-dependent quantum Hall particle collider to reveal fractional statistics in the Laughlin sequence(2023) Varada, Sushanth; Chalmers tekniska högskola / Institutionen för mikroteknologi och nanovetenskap (MC2); Chalmers University of Technology / Department of Microtechnology and Nanoscience (MC2); Splettstoesser, Janine; Acciai, Matteo; Spånslätt, ChristianElementary particles in nature (3+1 dimensions) are classified into bosons and fermions based on their exchange statistics. However, more general statistics, intermediate be- tween fermionic and bosonic, are possible in 2+1 dimensions. Quasiparticles obeying this intermediary statistics are called anyons. A particularly relevant phase of matter hosting anyons is the fractional quantum Hall effect, where anyonic statistics has recently been demonstrated. Generally, exchange statistics is expected to be accessible in interference experiments, such as in the Hong-Ou-Mandel effect. In this setup, fermions show van- ishing current correlations due to anti-bunching caused by the Pauli exclusion principle. Bosons, instead, bunch together due to Bose-Einstein statistics causing a surge in the current correlations. Can Hong-Ou-Mandel interferometry be extended to probe the frac- tional statistics of anyons? In this thesis, we investigate this question in a fractional quantum Hall setup in the Laughlin sequence (filling factor ν = 1/(2n + 1), n ∈ Z+), where two anyons collide at a quantum point contact with a tunable time delay. Previous studies investigating sim- ilar systems relate current correlations of quasiparticle collisions with braiding between injected anyons and quasi-particle-hole excitations at the tunneling quantum point con- tact, which emerge due to thermal or quantum fluctuations. However, it remains unclear whether the presently studied Hong-Ou-Mandel effect probes the universal exchange phase (θ) picked up by the quasiparticles or other parameters, such as the non-universal scaling dimension (δ). We show that θ accumulated by the incoming anyons due to interaction with quasi-particle-hole pairs at the quantum point contact cancel out in time-sensitive two-particle interferometry. Instead, the key quantity measured through current correla- tions is the non-universal δ of the quasi-particle-hole excitations.